#harwood — Public Fediverse posts

The Day the Micro-Rotor Was Introduced: Buren Super Slender and Universal Microtor

On February 18, 1958, representatives from Buren Watch Company and Universal Genève announced “the greatest technical advance in 30 years,” the micro-rotor automatic watch movement. This joint announcement, and the actions of the inventors and companies before and after it, contradict the oft-repeated story of conflict between them. In fact, the invention and introduction was friendly, thanks to the cordial Hans Kocher, who invented the micro-rotor yet allowed others to share the limelight and the credit.

Debunking the Legend

Like so many areas of watchmaking history, the story of the micro-rotor automatic watch is rich with folklore. And like too many other topics, most of those stories are flat-out wrong. I have been hearing this particular story for years, and was shocked to find that it is entirely contradicted by the plain facts published at the time.

Here’s the gist of what I was told about the launch of the Buren and Universal micro-rotor movements:

• Buren was first to market, introducing their micro-rotor movement in 1957 or maybe even 1954
• Universal infringed on Buren’s patent, didn’t have the technical expertise to design a new movement, and maybe never even had a patent of their own
• Buren sued Universal or tried to block them from marketing the Microtor
• And inexplicably that Universal actually produced the Buren movement because they couldn’t get it to work

None of this is remotely true.

• Technician-watchmaker Hans Kocher of Buren Watch Company invented the micro-rotor movement, filing a patent in 1954
• Jean-Michel Froidevaux and Fred Bandi, skilled technician-watchmakers at Universal, independently invented their own micro-rotor technology, filing a patent just 11 months later
• Kocher and Bandi collaborated on the launch, co-authoring an article on the technology and writing about each other’s work in supportive terms
• Buren and Universal announced their work at a joint press conference on February 18, 1958 and released their micro-rotor watches at the Basel Fair that year
• The companies targeted different markets and there is no sign of a lawsuit or any acrimony
• Both companies, along with Piaget, continued actively to develop micro-rotor movement technology for over a decade
• The technology was abandoned after both were purchased by American companies more interested in quartz electronic watches

So let’s sit back and enjoy the true story of the development of the micro-rotor watch movement!

The Rise of Self-Winding Watches

Le Locle watchmaker Abraham-Louis Perrelet is usually credited for building the first self-winding watch in the 1770s. Many1 have questioned the primacy of Perrelet’s “montre à secousses” (“shaking watch”), but many subsequent watchmakers, including Abraham-Louis Breguet, Louis Recordin, and the Jaquet-Droz family, claimed to have been inspired by his design. Perrelet’s watch used a weight mounted to the side of the movement, causing it to shake when moved. The concept of automatic winding (and even the name “perpetual”) were widely known through the 19th century but such a complex mechanism was deemed unnecessary to bring to market.

After World War I, Englishman John Harwood saw a need for self-winding watch. Soldiers were increasingly wearing wristwatches, and these were often damaged by moisture and dust. Inspired by a playground see-saw, Harwood independently2 invented a rocking weight segment that could wind the watch without a hole in the case. He patented the concept in 1923, built a prototype using a Blancpain movement, and brought the Harwood Perpetual to market with the help of A. Schild and Fortis of Grenchen. The watch only went into production late in the decade, and just a few thousand were produced before the Great Depression soon spelled the end.

You might also enjoy reading about “The Backward Evolution of the Rotating Bezel“

Harwood showed that the advent of the wristwatch had created customer demand for a self-winding movement, and the race was on to deliver a more practical one. I previously wrote about Eugène Meylan’s automatic winding mechanism, which was sold by Glycine starting in 1931. Another early player in automatic watches was Blancpain, which built a patented sliding watch called the Rolls for the French firm, Léon Hatot. Another modestly-successful automatic watch in this period was the Wig-Wag, which used the motion of the movement relative to the strap to wind the watch. But these oddball automatics soon fell by the wayside3.

It was the Rolex Oyster Perpetual that brought together all of the elements of the modern automatic wristwatch. Introduced about 19344, Rolex used a centrally-mounted rotor and winding mechanism stacked on top of their excellent movement. This technique was impractical in a pocket watch (which tended to sit vertically in a pocket) but made much more sense when strapped to a wrist. But the Rolex Oyster Perpetual movement was so thick it had to be mounted in a so-called “bubble-back” expanded case.

Seeing their success, especially though World War II, every Swiss company was racing to compete with Rolex with their own waterproof automatic watch. Felsa’s 1947 Bidynator brought bi-directional winding to the table5, ETA’s 1948 Eternamatic showed the potential of a rotor supported by ball bearings6, and Patek Philippe developed a “circumferential” rotor that extended down and around the movement. But all of these mechanisms added thickness, even as stylish consumers of the 1950s demanded ever-thinner watches. But making a thin automatic watch was inconceivable until the late 1950s, and the slimmest offerings (Zenith’s Cal. 133 and Movado’s Cal. 331) were bumper automatic movements, thin by accident rather than intentional design.

Hans Kocher and the Micro-Rotor

Hans Kocher grew up in the shadow of the H. Williamson watch factory in Büren an der Aare, Switzerland. He ran errands for the company as a young boy, and his work ethic so impressed the company’s chairman that he was sent to London to learn the business. But Kocher’s life took a turn when he met Austrian-born Josefine Rinner, a confectionary entrepreneur living in Zürich. The couple moved to Spain after the war, and their son (also named Hans) was born there in 1919. Kocher only settled down in 1923, marrying Josefine and returning to Bienne to work for the Williamson company. But the factory was bankrupt by 1931, with a group of local businessmen purchasing it. They invited Hans Kocher to return to Büren to take over management of the factory in 1932, and he spent the rest of his career there.

But this is the story of the younger Hans Kocher, who apprenticed in Büren before studying at the Technical school in Bienne. Following World War II, young Hans Kocher moved to Saint-Imier and worked in the technical department of the nearby Cortébert Watch Company. He was a wunderkind, filing patents, developing a central-seconds movement, and reorganizing the company’s manufacturing process. In 1951, after he proved himself, Kocher returned home to become technical director of the Buren Watch Company7.

Kocher believed that technology could elevate Buren in the competitive Swiss watch market and decided to build the best-possible automatic watch movement. Although many aspects of automatic winding were already patented by others, he saw an opportunity to address some of the shortcomings of contemporary automatic watches. For example, Kocher invented a mechanism to allow an automatic watch to be wound by hand, addressing widespread anxiety about power reserve. He also invented a few different bi-directional winding mechanisms and a more effective jewel pivot.

Another Kocher invention seemed to go nowhere: He embedded a tiny rotor inside the main winding rotor, creating a “Tilt-A-Whirl” effect to accelerate startup. Although this didn’t make it into production, this was the first glimpse of a micro-rotor winding system. A month later, Kocher filed a patent that he would later call his greatest work.

On June 21, 1954, Buren Watch Company filed a patent for a fully-realized micro-rotor automatic watch movement. Rather than adding a rotor on top of an existing movement, Hans Kocher redesigned the entire ebauche, reorganizing the wheel train to sink a tiny rotor inside. This was much more than a re-packaging effort, with nearly every component re-designed.

It would take nearly four years of development to bring the micro-rotor movement to market. The Swiss government had largely restricted companies from producing their own ebauches, but this was allowed for in-house and complicated movements. And the micro-rotor was indeed a very complicated movement, requiring entirely new design and tooling to be installed at the factory in Büren!

Kocher’s original micro-rotor movement design was elegant and symmetrical, already quite well-developed even in 1954. He called it a “planetary rotor” because he thought it resembled the planetary gearsets in automatic transmissions. But he spent years working on the construction and mechanics of the rotor and the exact arrangement of the wheels and bridges. And he soon had an unexpected collaborator.

Universal, Froidevaux, and Bandi

On May 27, 1955, Manufacture des Montres Universal of Geneva filed a remarkably similar patent for a micro-rotor movement. This was 11 months after Buren’s filing, yet three years before either patent would be published. Although the Swiss patent is un-signed, the American patent specifies that the inventors were Jean-Michel Froidevaux and Fred Bandi, two technician-watchmakers even younger than Hans Kocher. Both were incredibly talented and had made numerous inventions related to automatic watch winding and other areas of horology.

Patek Philippe filed for a patent their own micro-rotor movement in 1975, bringing their Cal. 240 to market a few years later. It has been continually updated and is one of the most-loved movements by enthusiasts like me. Chopard Manufacture leaned into the micro-rotor concept with the launch of the L.U.C movements in 1997, and it remains a highlight of the company’s offerings. A new Universal Genève launched in 2005, bringing a new Microtor (Cal. UG-100) to market in 2006. Schwarz Etienne and Parmigiani Fleurier both introduced new micro-rotor movements in 2010, and both supply these to other fine watch makers to this day. Armin Strom, Hermès, Girard-Perregaux, Bulgari, and many others have also released high-end micro-rotor movements. And Piaget never stopped developing their micro-rotor movements.

At a glance, the Universal patent looks very similar to Buren’s, but a closer examination shows that nearly every aspect of the design is different. The American patent authorities examined it closely, rejecting only the most broad claim made by Universal. Given these differences, and the evident skills and imagination of Froidevaux and Bandi, I believe that it was independently invented.

Froidevaux left Universal by 1956, just as the company was developing the micro-rotor watch movement for production. This was the same year that Universal opened its own new factory near Geneva, severing ties with the chronograph factory in Ponts-de-Martel that had been the source of complicated in-house movements for Universal since 1941. The new Carouge-Genève factory was likely outfitted with new machinery to produce the micro-rotor, along with other in-house movements developed by Fred Bandi.

It is very likely that the amiable Hans Kocher knew of the work underway in Geneva by this time, and he may have offered Fred Bandi some technical advice. Indeed, we know that the two collaborated on a paper outlining the benefits of the micro-rotor movement, which was published in the September/October 1957 edition of Journal Suisse d’Horlogerie. They cite the improvements gained by this design in reducing movement height, stress on the rotor bearings, and ease of servicing.

Up this point the thinnest automatic watch movements (Zénith’s Cal. 133 and Movado’s Cal. 331) had “bumper” movements rather than a free rotor. This is no surprise – the “sandwich stack” required to have a free rotor was inherently thicker than a winding mass that sat on the same plane as the wheel train and balance. But no bumper movement could match a micro-rotor embedded completely into the ebauche. Although not much thinner than hand-winding movements, the Büren and Universal movements were 20% thinner than most automatics at 4.1 to 4.2 mm8.

The Joint Release of the Buren Super Slender and Universal Microtor

On February 18, 1958, Raoul Perret of Universal Genève and Hans Kocher of the Buren Watch Company held a joint press conference in Geneva to announce “the greatest technical advance in 30 years.” Journalists from the major Swiss papers and industry journals learned about the revolutionary new micro-rotor technology, that would enable the companies to deliver the thinnest self-winding watches in the world. The companies promised that new watches using these movements would be released at the Basel Fair in April.

Ten days before the fair, on April 2, 1958, the Swiss paper Neue Zürcher Zeitung published an article with more detail on the technology of these new movements. Noting that “the fundamental concept behind this novel winding mechanism is identical in both designs,” the article praises both companies’ products, noting that “the specific technical solutions employed differ significantly.” This article was written by Fred Bandi, Technical Director for Universal Genève. Hans Kocher also wrote articles about the two companies’ launches, both independently and jointly with Bandi.

Finally, on April 12, 1958, the Basel Fair opened, with both companies showcasing watches housing their new micro-rotor movements. They even placed a joint advertisement in the Journal Suisse d’Horlogerie, featuring the logos of both companies.

The Buren Watch Company showed off their new Super Slender watch line at the fair, featuring Cal. 1000. This was a new ultra-thin watch line with a case meant to make the most of their “thinnest-ever” automatic watch movement. Confusingly, the company’s Basel Fair booth was a generic paean to post-war globalization, dedicated to the theme “l’universalité.” The new Super Slender movement was depicted on a small card at the corner, with the ultra-thin watches arranged among other more mundane products.

Universal Genève presented a strong contrast, dedicating their entire display to the new Microtor movement. They even built a large model in a transparent plexiglass case, demonstrating the internal relationship between the micro-rotor and wheel train. The new Cal. 215 was used in an existing product line, the Polerouter (which had been introduced as “Polarouter” in 1954). Although Universal offered new dial designs for 1958, the Microtor’s slimmer profile was not leveraged for a watch that was notably thin.

Both watches were brought to market in the following months with no hint of production delays. They are widely seen and advertised over the next few years in press coverage, company advertising, and retail promotion. For example, an April 1958 ad for international retailer Turler lists the Universal Polerouter Microtor for 270 francs in steel or 820 francs in gold. Meanwhile, the Buren Super Slender was advertised in 1959 for 170 francs in steel or 185 francs for the model with a calendar complication, called Cal. 1001.

What Happened Next

Buren and Universal leaned heavily into their micro-rotor watch movements for the next few years, developing and updating them continually. And two more ultra-thin automatic movements appeared at Basel in 1959 and 1960: The Sandoz 333, which used a peripheral rotor movement designed by FHF, and Piaget’s knock-out 2.3 mm thin micro-rotor Cal. 12 P. But the introduction of the Bulova Accutron on October 25, 1960 upended the entire industry.

Buren actually introduced two micro-rotor movements at Basel in 1958: The base Cal. 1000 was truly “super slender” at 4.2 mm, but they also showed Cal. 1001, which added a date complication and 0.6 mm thickness. Although not as revolutionary as the micro-rotor, Paul Marmier’s patented date mechanism was quite innovative. It used an eccentric cam to keep the advance finger safely back from the date wheel teeth to avoid the risk of damage. The date advanced in just 12 minutes at midnight, and the mechanism also allowed quicker setting of the date by moving the time back to 11:30.

By 1959 Buren added Cal. 1002 and 1003, which featured a thinner balance cock to make way for an elongated wheel train bridge screwed to the base plate for greater stability. The original Cal. 1000 and 1001 remained in production, however, into the 1960s.

Universal added a date complication as well, though theirs added over 1 mm to the thickness of the base Cal. 215. This did not pose an issue because the Microtor was used in watches of more ordinary thickness like the Polerouter Date. But the Geneva company did finally lean into the thin profile of the basic Microtor movement with the new 1959 Polerouter Jet, boasting that it was as thin as a hand-winding watch and the thinnest waterproof automatic watch in the world. Universal put the Microtor-Calendrier movement on a diet over the next few years, beveling the edges and slimming it to 4.7 mm (once again 0.1 mm thinner than the competing Buren movement). And Universal proved the robustness of their movement by equipping members of the Swiss Greenland Expedition with Microtor-powered Polerouters during the International Geophysical Year.

Other watches had previously been advertised for their ultra-thin profile, including Omega’s Centenaire and Cyma’s Navystar, but Movado, Sandoz, and Piaget were the strongest contenders. Movado had claimed the crown for the thinnest watch in 1935 with the Novoplan and delivered the automatic Cal. 331 in 1952, which was just 4.3 mm thick thanks to a beveled bumper rotor.

Sandoz announced the “thinnest waterproof watch” in 1954 with their hand-winding Cal. 55, allowing them to produce a 6.9 mm watch. And they saw an opportunity in a peripheral rotor concept under development at the Fabrique d’Horlogerie de Fontainemelon. Unaware of the micro-rotor8, Sandoz and FHF targeted the 1959 Basel Fair to launch this new ultra-thin automatic watch. Despite being upstaged, the Sandoz 333 remains the first peripheral-winding automatic watch to market.

Piaget claimed outright victory for the thinnest watch in 1957 with the 4 mm Ref. 904, housing the 2.0 mm Cal. 9 P. Valentin Piaget of their specialist movement maker Complications SA saw unrealized potential in the micro-rotor concept. His Cal. 12 P, patented in 1958 and announced at the Basel Fair in 1960, dispensed with the center wheel and radically sliced away the ebauche. Measuring just 2.3 mm thick, this movement allowed Piaget’s Ref. 12 watches to stay at just 4 mm thick overall. Piaget has remained committed to this design, producing Cal. 1200 to this day!

Buren embraced Piaget’s ideas, and their Cal. 1280 was similarly stripped-down, coming in at just 2.85 mm thick. This was used in their modern Intra Matic9 line, launched at the Basel Fair in 1965. Variations with date and central seconds ranged up to 3.60 mm, still over half a millimeter thinner than their original Super Slender.

The Intramatic movement made history on March 3, 1969 when Hans Kocher10 and Gerald Dubois announced the Chronomatic movement, built on Buren’s micro-rotor ebauche. This would be the first Swiss automatic chronograph in customer hands, used by Breitling, Heuer, and Hamilton, which had purchased Buren in February of 1966. Hamilton-Buren was taken over by the SIHH group in 1971 and the once-great Büren factory was closed the following year, with all assets sold. This came just as the Chronomatic was gaining market traction and sadly just before the launch of Buren’s great Calbre 8211.

Universal also collaborated with Piaget, filing a joint patent in March of 1959 for a slim ratcheting winding system for micro-rotor movements. They continually updated their Microtor movement line, culminating in the 1966 introduction of the re-designed Cal. 66. Unlike the hand-made Piaget Cal. 12 P, the new Universal and Buren movements were designed for mass production and daily wear. And Universal once again beat Buren’s mark, with their ebauche measuring just 2.50 mm thick. This time Universal leaned into the thinness of the movement, matching Piaget with a new Golden Shadow watch line just 4 mm thick.

Everything changed for Universal in August of 1966, as the Bulova Watch Company of New York purchased the company. Flush with cash from the Accutron, a global phenomenon never before seen in watchmaking, Bulova sought to solidify its control over the luxury watch industry by bringing the Geneva firm under its control. Universal continued production of the Microtor family into the 1970s and even developed the world’s thinnest quartz movement in 197512. But Bulova was slow to embrace quartz as the market for the Accutron evaporated. The Universal factory in Geneva was bankrupt by the late 1970s and was sold in 1983 to new investors.

The Micro-Rotor Lives On

The micro-rotor is not dead. Far from it: There are more micro-rotor movements on the market today than ever before!

Universal was re-launched as an upscale sister brand to Breitling on April 8, 2026 and two new Microtor movements form the core of the new offerings. The new double-barrel Polerouter Microtor is a lovely tribute to Hans Kocher, who was deeply involved in both innovations. And the new Compax Microtor movement recalls the pioneering Chronomatic movement.

Research Notes

1. The question of whether Perrelet was the first to create a self-winding watch was a matter of great interest through the 20th century. Historian Alfred Chapuis uncovered many prior and subsequent designs, yet he concluded in his seminal book “La Montre Automatique Ancienne” that Perrelet absolutely deserved the credit. That being said, the self-winding watch “discovered” by Léon Leroy of Paris in 1949 may not have been created by Perrelet, according to a 1996 Europa Star article by Jean-Claude Nicolet with rebuttal by Jean-Claude Sabrier.
2. Not being a watch industry insider, Harwood may have been completely unaware that dozens of watchmakers had developed self-winding watches for over a century prior to his invention. And L. Leroy of Paris had already produced a self-winding wristwatch a year before Harwood’s patent. But he was the first to recognize the market for a wristwatch with a sealed case and self-winding movement.
3. The sliding weight concept was actually successfully revived by Pierce just after World War II. This “dissident” Moutier firm was unwilling to abide by the Swiss cartel’s production quotas, so they were blocked from working with nearly every other company. So they developed their own slim sliding-weight automatic, an amazing in-house chronograph movement, and more! In modern times we have seen another sliding-weight automatic, the Corum Golden Bridge Automatic.
4. I’m not a Rolex expert, but I am confounded by the lack of definitive history for this most-important watchmaker. The earliest mention I could find of the Oyster Perpetual comes from Journal Suisse d’Horlogerie in September of 1934, and it was fully illustrated in January of 1936. Given that Rolex trademarked the name in 1932, I guess that places the introduction of the Rolex Perpetual movement in 1933 or 1934. It definitely wasn’t 1931, despite countless blog posts and Rolex’s own advertising.
5. Incredibly, some of the earliest known self-winding pocket watch movements also have clever bi-directional winding solutions: The four controversial maybe-Perrelet movements have a pawl winding system similar to the much-later Pellaton and Magic Lever, and many of the “shaker” movements had bi-directional winding too. But Felsa’s elegant Bidynator inspired the whole industry to adopt this concept. Surprisingly, modern movements are dropping bi-directional winding, finding that it’s not actually all that useful.
6. Ball bearing support for a winding rotor was patented in 1929. But these typically placed the bearings at the periphery, supporting the rotor itself. ETA’s original Eternamatic was a tiny movement for ladies watches so the engineers brought the ball bearings to the center. Seeing how well it worked, the “five balls” became the logo of Eterna!
7. I should clarify that the name of the town is “Büren an der Aare” and it is commonly called “Büren”. But the brand name of the watch company, officially adopted by H. Williamson in 1916, was “Buren Watch Company” without the umlaut. This was generally used by the company through the 1960s, though they sometimes did include the umlaut in advertising and public communication. Confusingly, most patents list it using the Anglicized form of the name of the town, “Bueren Watch Company.” I try to be consistent (or perhaps confusing) and use “Büren” to refer to the town and “Buren” to refer to the company.
8. Oops! The Fabrique d’Horlogerie de Fontainemelon was working on another thin automatic winding system at the same time, filing patents on their peripheral rotor on September 11, 1956. This was before the announcement or publication of the micro-rotor, and they no-doubt thought that their “Fontomatic” Cal. 65 would be the thinnest automatic movement at just 4.5 mm. This came to market in 1959 as the Sandoz 333, and advertisements for this latecomer specifically neglect to mention that number, which was surpassed a year earlier by both Buren and Universal.
9. Buren trademarked “Intra Matic” in 1964 and used this name in the 1965 launch. But they also used “Intramatic” in this period, variously using both names. They had a sub-model called the “Intramatic Polestar” or “Intra Matic Pole-Star” in the 1960s as well, and I can’t imagine Universal loved this name.
10. This would be Hans Kocher-Aeschbacher, the son, rather than his father Hans Kocher-Rinner, who retired that same year. The younger Hans Kocher was a truly remarkable man, deserving of a Prix Gaïa award in all three categories: Watchmaker, businessman, and historian. He was also incredibly magnanimous, not giving undue attention in his industry history writing and speaking to the Buren “planetary rotor” despite considering it his life’s greatest work.
11. I’m wearing my Buren Calibre 82 watch as I write this!
12. The 1975 Golden Shadow and White Shadow Quartz movement measured 3.45 mm thick. It was rapidly surpassed by Citizen, just under 1 mm in 1978, Seiko, 0.90 mm that same year, and the incredible Swiss Delirium movements.

The Day the Micro-Rotor Was Introduced: Buren Super Slender and Universal Microtor

On February 18, 1958, representatives from Buren Watch Company and Universal Genève announced “the greatest technical advance in 30 years,” the micro-rotor automatic watch movement. This joint announcement, and the actions of the inventors and companies before and after it, contradict the oft-repeated story of conflict between them. In fact, the invention and introduction was friendly, thanks to the cordial Hans Kocher, who invented the micro-rotor yet allowed others to share the limelight and the credit.

Debunking the Legend

Like so many areas of watchmaking history, the story of the micro-rotor automatic watch is rich with folklore. And like too many other topics, most of those stories are flat-out wrong. I have been hearing this particular story for years, and was shocked to find that it is entirely contradicted by the plain facts published at the time.

Here’s the gist of what I was told about the launch of the Buren and Universal micro-rotor movements:

• Buren was first to market, introducing their micro-rotor movement in 1957 or maybe even 1954
• Universal infringed on Buren’s patent, didn’t have the technical expertise to design a new movement, and maybe never even had a patent of their own
• Buren sued Universal or tried to block them from marketing the Microtor
• And inexplicably that Universal actually produced the Buren movement because they couldn’t get it to work

None of this is remotely true.

• Technician-watchmaker Hans Kocher of Buren Watch Company invented the micro-rotor movement, filing a patent in 1954
• Jean-Michel Froidevaux and Fred Bandi, skilled technician-watchmakers at Universal, independently invented their own micro-rotor technology, filing a patent just 11 months later
• Kocher and Bandi collaborated on the launch, co-authoring an article on the technology and writing about each other’s work in supportive terms
• Buren and Universal announced their work at a joint press conference on February 18, 1958 and released their micro-rotor watches at the Basel Fair that year
• The companies targeted different markets and there is no sign of a lawsuit or any acrimony
• Both companies, along with Piaget, continued actively to develop micro-rotor movement technology for over a decade
• The technology was abandoned after both were purchased by American companies more interested in quartz electronic watches

So let’s sit back and enjoy the true story of the development of the micro-rotor watch movement!

The Rise of Self-Winding Watches

Le Locle watchmaker Abraham-Louis Perrelet is usually credited for building the first self-winding watch in the 1770s. Many1 have questioned the primacy of Perrelet’s “montre à secousses” (“shaking watch”), but many subsequent watchmakers, including Abraham-Louis Breguet, Louis Recordin, and the Jaquet-Droz family, claimed to have been inspired by his design. Perrelet’s watch used a weight mounted to the side of the movement, causing it to shake when moved. The concept of automatic winding (and even the name “perpetual”) were widely known through the 19th century but such a complex mechanism was deemed unnecessary to bring to market.

After World War I, Englishman John Harwood saw a need for self-winding watch. Soldiers were increasingly wearing wristwatches, and these were often damaged by moisture and dust. Inspired by a playground see-saw, Harwood independently2 invented a rocking weight segment that could wind the watch without a hole in the case. He patented the concept in 1923, built a prototype using a Blancpain movement, and brought the Harwood Perpetual to market with the help of A. Schild and Fortis of Grenchen. The watch only went into production late in the decade, and just a few thousand were produced before the Great Depression soon spelled the end.

You might also enjoy reading about “The Backward Evolution of the Rotating Bezel“

Harwood showed that the advent of the wristwatch had created customer demand for a self-winding movement, and the race was on to deliver a more practical one. I previously wrote about Eugène Meylan’s automatic winding mechanism, which was sold by Glycine starting in 1931. Another early player in automatic watches was Blancpain, which built a patented sliding watch called the Rolls for the French firm, Léon Hatot. Another modestly-successful automatic watch in this period was the Wig-Wag, which used the motion of the movement relative to the strap to wind the watch. But these oddball automatics soon fell by the wayside3.

It was the Rolex Oyster Perpetual that brought together all of the elements of the modern automatic wristwatch. Introduced about 19344, Rolex used a centrally-mounted rotor and winding mechanism stacked on top of their excellent movement. This technique was impractical in a pocket watch (which tended to sit vertically in a pocket) but made much more sense when strapped to a wrist. But the Rolex Oyster Perpetual movement was so thick it had to be mounted in a so-called “bubble-back” expanded case.

Seeing their success, especially though World War II, every Swiss company was racing to compete with Rolex with their own waterproof automatic watch. Felsa’s 1947 Bidynator brought bi-directional winding to the table5, ETA’s 1948 Eternamatic showed the potential of a rotor supported by ball bearings6, and Patek Philippe developed a “circumferential” rotor that extended down and around the movement. But all of these mechanisms added thickness, even as stylish consumers of the 1950s demanded ever-thinner watches. But making a thin automatic watch was inconceivable until the late 1950s, and the slimmest offerings (Zenith’s Cal. 133 and Movado’s Cal. 331) were bumper automatic movements, thin by accident rather than intentional design.

Hans Kocher and the Micro-Rotor

Hans Kocher grew up in the shadow of the H. Williamson watch factory in Büren an der Aare, Switzerland. He ran errands for the company as a young boy, and his work ethic so impressed the company’s chairman that he was sent to London to learn the business. But Kocher’s life took a turn when he met Austrian-born Josefine Rinner, a confectionary entrepreneur living in Zürich. The couple moved to Spain after the war, and their son (also named Hans) was born there in 1919. Kocher only settled down in 1923, marrying Josefine and returning to Bienne to work for the Williamson company. But the factory was bankrupt by 1931, with a group of local businessmen purchasing it. They invited Hans Kocher to return to Büren to take over management of the factory in 1932, and he spent the rest of his career there.

But this is the story of the younger Hans Kocher, who apprenticed in Büren before studying at the Technical school in Bienne. Following World War II, young Hans Kocher moved to Saint-Imier and worked in the technical department of the nearby Cortébert Watch Company. He was a wunderkind, filing patents, developing a central-seconds movement, and reorganizing the company’s manufacturing process. In 1951, after he proved himself, Kocher returned home to become technical director of the Buren Watch Company7.

Kocher believed that technology could elevate Buren in the competitive Swiss watch market and decided to build the best-possible automatic watch movement. Although many aspects of automatic winding were already patented by others, he saw an opportunity to address some of the shortcomings of contemporary automatic watches. For example, Kocher invented a mechanism to allow an automatic watch to be wound by hand, addressing widespread anxiety about power reserve. He also invented a few different bi-directional winding mechanisms and a more effective jewel pivot.

Another Kocher invention seemed to go nowhere: He embedded a tiny rotor inside the main winding rotor, creating a “Tilt-A-Whirl” effect to accelerate startup. Although this didn’t make it into production, this was the first glimpse of a micro-rotor winding system. A month later, Kocher filed a patent that he would later call his greatest work.

On June 21, 1954, Buren Watch Company filed a patent for a fully-realized micro-rotor automatic watch movement. Rather than adding a rotor on top of an existing movement, Hans Kocher redesigned the entire ebauche, reorganizing the wheel train to sink a tiny rotor inside. This was much more than a re-packaging effort, with nearly every component re-designed.

It would take nearly four years of development to bring the micro-rotor movement to market. The Swiss government had largely restricted companies from producing their own ebauches, but this was allowed for in-house and complicated movements. And the micro-rotor was indeed a very complicated movement, requiring entirely new design and tooling to be installed at the factory in Büren!

Kocher’s original micro-rotor movement design was elegant and symmetrical, already quite well-developed even in 1954. He called it a “planetary rotor” because he thought it resembled the planetary gearsets in automatic transmissions. But he spent years working on the construction and mechanics of the rotor and the exact arrangement of the wheels and bridges. And he soon had an unexpected collaborator.

Universal, Froidevaux, and Bandi

On May 27, 1955, Manufacture des Montres Universal of Geneva filed a remarkably similar patent for a micro-rotor movement. This was 11 months after Buren’s filing, yet three years before either patent would be published. Although the Swiss patent is un-signed, the American patent specifies that the inventors were Jean-Michel Froidevaux and Fred Bandi, two technician-watchmakers even younger than Hans Kocher. Both were incredibly talented and had made numerous inventions related to automatic watch winding and other areas of horology.

At a glance, the Universal patent looks very similar to Buren’s, but a closer examination shows that nearly every aspect of the design is different. The American patent authorities examined it closely, rejecting only the most broad claim made by Universal. Given these differences, and the evident skills and imagination of Froidevaux and Bandi, I believe that it was independently invented.

Froidevaux left Universal by 1956, just as the company was developing the micro-rotor watch movement for production. This was the same year that Universal opened its own new factory near Geneva, severing ties with the chronograph factory in Ponts-de-Martel that had been the source of complicated in-house movements for Universal since 1941. The new Carouge-Genève factory was likely outfitted with new machinery to produce the micro-rotor, along with other in-house movements developed by Fred Bandi.

It is very likely that the amiable Hans Kocher knew of the work underway in Geneva by this time, and he may have offered Fred Bandi some technical advice. Indeed, we know that the two collaborated on a paper outlining the benefits of the micro-rotor movement, which was published in the September/October 1957 edition of Journal Suisse d’Horlogerie. They cite the improvements gained by this design in reducing movement height, stress on the rotor bearings, and ease of servicing.

Up this point the thinnest automatic watch movements (Zénith’s Cal. 133 and Movado’s Cal. 331) had “bumper” movements rather than a free rotor. This is no surprise – the “sandwich stack” required to have a free rotor was inherently thicker than a winding mass that sat on the same plane as the wheel train and balance. But no bumper movement could match a micro-rotor embedded completely into the ebauche. Although not much thinner than hand-winding movements, the Büren and Universal movements were 20% thinner than most automatics at 4.1 to 4.2 mm8.

The Joint Release of the Buren Super Slender and Universal Microtor

On February 18, 1958, Raoul Perret of Universal Genève and Hans Kocher of the Buren Watch Company held a joint press conference in Geneva to announce “the greatest technical advance in 30 years.” Journalists from the major Swiss papers and industry journals learned about the revolutionary new micro-rotor technology, that would enable the companies to deliver the thinnest self-winding watches in the world. The companies promised that new watches using these movements would be released at the Basel Fair in April.

Ten days before the fair, on April 2, 1958, the Swiss paper Neue Zürcher Zeitung published an article with more detail on the technology of these new movements. Noting that “the fundamental concept behind this novel winding mechanism is identical in both designs,” the article praises both companies’ products, noting that “the specific technical solutions employed differ significantly.” This article was written by Fred Bandi, Technical Director for Universal Genève. Hans Kocher also wrote articles about the two companies’ launches, both independently and jointly with Bandi.

Finally, on April 12, 1958, the Basel Fair opened, with both companies showcasing watches housing their new micro-rotor movements. They even placed a joint advertisement in the Journal Suisse d’Horlogerie, featuring the logos of both companies.

The Buren Watch Company showed off their new Super Slender watch line at the fair, featuring Cal. 1000. This was a new ultra-thin watch line with a case meant to make the most of their “thinnest-ever” automatic watch movement. Confusingly, the company’s Basel Fair booth was a generic paean to post-war globalization, dedicated to the theme “l’universalité.” The new Super Slender movement was depicted on a small card at the corner, with the ultra-thin watches arranged among other more mundane products.

Universal Genève presented a strong contrast, dedicating their entire display to the new Microtor movement. They even built a large model in a transparent plexiglass case, demonstrating the internal relationship between the micro-rotor and wheel train. The new Cal. 215 was used in an existing product line, the Polerouter (which had been introduced as “Polarouter” in 1954). Although Universal offered new dial designs for 1958, the Microtor’s slimmer profile was not leveraged for a watch that was notably thin.

Both watches were brought to market in the following months with no hint of production delays. They are widely seen and advertised over the next few years in press coverage, company advertising, and retail promotion. For example, an April 1958 ad for international retailer Turler lists the Universal Polerouter Microtor for 270 francs in steel or 820 francs in gold. Meanwhile, the Buren Super Slender was advertised in 1959 for 170 francs in steel or 185 francs for the model with a calendar complication, called Cal. 1001.

What Happened Next

Buren and Universal leaned heavily into their micro-rotor watch movements for the next few years, developing and updating them continually. And two more ultra-thin automatic movements appeared at Basel in 1959 and 1960: The Sandoz 333, which used a peripheral rotor movement designed by FHF, and Piaget’s knock-out 2.3 mm thin micro-rotor Cal. 12 P. But the introduction of the Bulova Accutron on October 25, 1960 upended the entire industry.

Buren actually introduced two micro-rotor movements at Basel in 1958: The base Cal. 1000 was truly “super slender” at 4.2 mm, but they also showed Cal. 1001, which added a date complication and 0.6 mm thickness. Although not as revolutionary as the micro-rotor, Paul Marmier’s patented date mechanism was quite innovative. It used an eccentric cam to keep the advance finger safely back from the date wheel teeth to avoid the risk of damage. The date advanced in just 12 minutes at midnight, and the mechanism also allowed quicker setting of the date by moving the time back to 11:30.

By 1959 Buren added Cal. 1002 and 1003, which featured a thinner balance cock to make way for an elongated wheel train bridge screwed to the base plate for greater stability. The original Cal. 1000 and 1001 remained in production, however, into the 1960s.

Universal added a date complication as well, though theirs added over 1 mm to the thickness of the base Cal. 215. This did not pose an issue because the Microtor was used in watches of more ordinary thickness like the Polerouter Date. But the Geneva company did finally lean into the thin profile of the basic Microtor movement with the new 1959 Polerouter Jet, boasting that it was as thin as a hand-winding watch and the thinnest waterproof automatic watch in the world. Universal put the Microtor-Calendrier movement on a diet over the next few years, beveling the edges and slimming it to 4.7 mm (once again 0.1 mm thinner than the competing Buren movement). And Universal proved the robustness of their movement by equipping members of the Swiss Greenland Expedition with Microtor-powered Polerouters during the International Geophysical Year.

Other watches had previously been advertised for their ultra-thin profile, including Omega’s Centenaire and Cyma’s Navystar, but Movado, Sandoz, and Piaget were the strongest contenders. Movado had claimed the crown for the thinnest watch in 1935 with the Novoplan and delivered the automatic Cal. 331 in 1952, which was just 4.3 mm thick thanks to a beveled bumper rotor.

Sandoz announced the “thinnest waterproof watch” in 1954 with their hand-winding Cal. 55, allowing them to produce a 6.9 mm watch. And they saw an opportunity in a peripheral rotor concept under development at the Fabrique d’Horlogerie de Fontainemelon. Unaware of the micro-rotor8, Sandoz and FHF targeted the 1959 Basel Fair to launch this new ultra-thin automatic watch. Despite being upstaged, the Sandoz 333 remains the first peripheral-winding automatic watch to market.

Piaget claimed outright victory for the thinnest watch in 1957 with the 4 mm Ref. 904, housing the 2.0 mm Cal. 9 P. Valentin Piaget of their specialist movement maker Complications SA saw unrealized potential in the micro-rotor concept. His Cal. 12 P, patented in 1958 and announced at the Basel Fair in 1960, dispensed with the center wheel and radically sliced away the ebauche. Measuring just 2.3 mm thick, this movement allowed Piaget’s Ref. 12 watches to stay at just 4 mm thick overall. Piaget has remained committed to this design, producing Cal. 1200 to this day!

Buren embraced Piaget’s ideas, and their Cal. 1280 was similarly stripped-down, coming in at just 2.85 mm thick. This was used in their modern Intra Matic9 line, launched at the Basel Fair in 1965. Variations with date and central seconds ranged up to 3.60 mm, still over half a millimeter thinner than their original Super Slender.

The Intramatic movement made history on March 3, 1969 when Hans Kocher10 and Gerald Dubois announced the Chronomatic movement, built on Buren’s micro-rotor ebauche. This would be the first Swiss automatic chronograph in customer hands, used by Breitling, Heuer, and Hamilton, which had purchased Buren in February of 1966. Hamilton-Buren was taken over by the SIHH group in 1971 and the once-great Büren factory was closed the following year, with all assets sold. This came just as the Chronomatic was gaining market traction and sadly just before the launch of Buren’s great Calbre 8211.

Universal also collaborated with Piaget, filing a joint patent in March of 1959 for a slim ratcheting winding system for micro-rotor movements. They continually updated their Microtor movement line, culminating in the 1966 introduction of the re-designed Cal. 66. Unlike the hand-made Piaget Cal. 12 P, the new Universal and Buren movements were designed for mass production and daily wear. And Universal once again beat Buren’s mark, with their ebauche measuring just 2.50 mm thick. This time Universal leaned into the thinness of the movement, matching Piaget with a new Golden Shadow watch line just 4 mm thick.

Everything changed for Universal in August of 1966, as the Bulova Watch Company of New York purchased the company. Flush with cash from the Accutron, a global phenomenon never before seen in watchmaking, Bulova sought to solidify its control over the luxury watch industry by bringing the Geneva firm under its control. Universal continued production of the Microtor family into the 1970s and even developed the world’s thinnest quartz movement in 197512. But Bulova was slow to embrace quartz as the market for the Accutron evaporated. The Universal factory in Geneva was bankrupt by the late 1970s and was sold in 1983 to new investors.

The Micro-Rotor Lives On

The micro-rotor is not dead. Far from it: There are more micro-rotor movements on the market today than ever before!

Patek Philippe filed for a patent their own micro-rotor movement in 1975, bringing their Cal. 240 to market a few years later. It has been continually updated and is one of the most-loved movements by enthusiasts like me. Chopard Manufacture leaned into the micro-rotor concept with the launch of the L.U.C movements in 1997, and it remains a highlight of the company’s offerings. A new Universal Genève launched in 2005, bringing a new Microtor (Cal. UG-100) to market in 2006. Schwarz Etienne and Parmigiani Fleurier both introduced new micro-rotor movements in 2010, and both supply these to other fine watch makers to this day. Armin Strom, Hermès, Girard-Perregaux, Bulgari, and many others have also released high-end micro-rotor movements. And Piaget never stopped developing their micro-rotor movements.

Universal was re-launched as an upscale sister brand to Breitling on April 8, 2026 and two new Microtor movements form the core of the new offerings. The new Polerouter Microtor is the first double-barrel micro-rotor movement I know of, and is a lovely tribute to Hans Kocher, who was deeply involved in both innovations. And the new Compax Microtor movement recalls the pioneering Chronomatic movement.

Research Notes

1. The question of whether Perrelet was the first to create a self-winding watch was a matter of great interest through the 20th century. Historian Alfred Chapuis uncovered many prior and subsequent designs, yet he concluded in his seminal book “La Montre Automatique Ancienne” that Perrelet absolutely deserved the credit. That being said, the self-winding watch “discovered” by Léon Leroy of Paris in 1949 may not have been created by Perrelet, according to a 1996 Europa Star article by Jean-Claude Nicolet with rebuttal by Jean-Claude Sabrier.
2. Not being a watch industry insider, Harwood may have been completely unaware that dozens of watchmakers had developed self-winding watches for over a century prior to his invention. And L. Leroy of Paris had already produced a self-winding wristwatch a year before Harwood’s patent. But he was the first to recognize the market for a wristwatch with a sealed case and self-winding movement.
3. The sliding weight concept was actually successfully revived by Pierce just after World War II. This “dissident” Moutier firm was unwilling to abide by the Swiss cartel’s production quotas, so they were blocked from working with nearly every other company. So they developed their own slim sliding-weight automatic, an amazing in-house chronograph movement, and more! In modern times we have seen another sliding-weight automatic, the Corum Golden Bridge Automatic.
4. I’m not a Rolex expert, but I am confounded by the lack of definitive history for this most-important watchmaker. The earliest mention I could find of the Oyster Perpetual comes from Journal Suisse d’Horlogerie in September of 1934, and it was fully illustrated in January of 1936. Given that Rolex trademarked the name in 1932, I guess that places the introduction of the Rolex Perpetual movement in 1933 or 1934. It definitely wasn’t 1931, despite countless blog posts and Rolex’s own advertising.
5. Incredibly, some of the earliest known self-winding pocket watch movements also have clever bi-directional winding solutions: The four controversial maybe-Perrelet movements have a pawl winding system similar to the much-later Pellaton and Magic Lever, and many of the “shaker” movements had bi-directional winding too. But Felsa’s elegant Bidynator inspired the whole industry to adopt this concept. Surprisingly, modern movements are dropping bi-directional winding, finding that it’s not actually all that useful.
6. Ball bearing support for a winding rotor was patented in 1929. But these typically placed the bearings at the periphery, supporting the rotor itself. ETA’s original Eternamatic was a tiny movement for ladies watches so the engineers brought the ball bearings to the center. Seeing how well it worked, the “five balls” became the logo of Eterna!
7. I should clarify that the name of the town is “Büren an der Aare” and it is commonly called “Büren”. But the brand name of the watch company, officially adopted by H. Williamson in 1916, was “Buren Watch Company” without the umlaut. This was generally used by the company through the 1960s, though they sometimes did include the umlaut in advertising and public communication. Confusingly, most patents list it using the Anglicized form of the name of the town, “Bueren Watch Company.” I try to be consistent (or perhaps confusing) and use “Büren” to refer to the town and “Buren” to refer to the company.
8. Oops! The Fabrique d’Horlogerie de Fontainemelon was working on another thin automatic winding system at the same time, filing patents on their peripheral rotor on September 11, 1956. This was before the announcement or publication of the micro-rotor, and they no-doubt thought that their “Fontomatic” Cal. 65 would be the thinnest automatic movement at just 4.5 mm. This came to market in 1959 as the Sandoz 333, and advertisements for this latecomer specifically neglect to mention that number, which was surpassed a year earlier by both Buren and Universal.
9. Buren trademarked “Intra Matic” in 1964 and used this name in the 1965 launch. But they also used “Intramatic” in this period, variously using both names. They had a sub-model called the “Intramatic Polestar” or “Intra Matic Pole-Star” in the 1960s as well, and I can’t imagine Universal loved this name.
10. This would be Hans Kocher-Aeschbacher, the son, rather than his father Hans Kocher-Rinner, who retired that same year. The younger Hans Kocher was a truly remarkable man, deserving of a Prix Gaïa award in all three categories: Watchmaker, businessman, and historian. He was also incredibly magnanimous, not giving undue attention in his industry history writing and speaking to the Buren “planetary rotor” despite considering it his life’s greatest work.
11. I’m wearing my Buren Calibre 82 watch as I write this!
12. The 1975 Golden Shadow and White Shadow Quartz movement measured 3.45 mm thick. It was rapidly surpassed by Citizen, just under 1 mm in 1978, Seiko, 0.90 mm that same year, and the incredible Swiss Delirium movements.

The Day the Micro-Rotor Was Introduced: Buren Super Slender and Universal Microtor

On February 18, 1958, representatives from Buren Watch Company and Universal Genève announced “the greatest technical advance in 30 years,” the micro-rotor automatic watch movement. This joint announcement, and the actions of the inventors and companies before and after it, contradict the oft-repeated story of conflict between them. In fact, the invention and introduction was friendly, thanks to the cordial Hans Kocher, who invented the micro-rotor yet allowed others to share the limelight and the credit.

Debunking the Legend

Like so many areas of watchmaking history, the story of the micro-rotor automatic watch is rich with folklore. And like too many other topics, most of those stories are flat-out wrong. I have been hearing this particular story for years, and was shocked to find that it is entirely contradicted by the plain facts published at the time.

Here’s the gist of what I was told about the launch of the Buren and Universal micro-rotor movements:

• Buren was first to market, introducing their micro-rotor movement in 1957 or maybe even 1954
• Universal infringed on Buren’s patent, didn’t have the technical expertise to design a new movement, and maybe never even had a patent of their own
• Buren sued Universal or tried to block them from marketing the Microtor
• And inexplicably that Universal actually produced the Buren movement because they couldn’t get it to work

None of this is remotely true.

• Technician-watchmaker Hans Kocher of Buren Watch Company invented the micro-rotor movement, filing a patent in 1954
• Jean-Michel Froidevaux and Fred Bandi, skilled technician-watchmakers at Universal, independently invented their own micro-rotor technology, filing a patent just 11 months later
• Kocher and Bandi collaborated on the launch, co-authoring an article on the technology and writing about each other’s work in supportive terms
• Buren and Universal announced their work at a joint press conference on February 18, 1958 and released their micro-rotor watches at the Basel Fair that year
• The companies targeted different markets and there is no sign of a lawsuit or any acrimony
• Both companies, along with Piaget, continued actively to develop micro-rotor movement technology for over a decade
• The technology was abandoned after both were purchased by American companies more interested in quartz electronic watches

So let’s sit back and enjoy the true story of the development of the micro-rotor watch movement!

The Rise of Self-Winding Watches

Le Locle watchmaker Abraham-Louis Perrelet is usually credited for building the first self-winding watch in the 1770s. Many1 have questioned the primacy of Perrelet’s “montre à secousses” (“shaking watch”), but many subsequent watchmakers, including Abraham-Louis Breguet, Louis Recordin, and the Jaquet-Droz family, claimed to have been inspired by his design. Perrelet’s watch used a weight mounted to the side of the movement, causing it to shake when moved. The concept of automatic winding (and even the name “perpetual”) were widely known through the 19th century but such a complex mechanism was deemed unnecessary to bring to market.

After World War I, Englishman John Harwood saw a need for self-winding watch. Soldiers were increasingly wearing wristwatches, and these were often damaged by moisture and dust. Inspired by a playground see-saw, Harwood independently2 invented a rocking weight segment that could wind the watch without a hole in the case. He patented the concept in 1923, built a prototype using a Blancpain movement, and brought the Harwood Perpetual to market with the help of A. Schild and Fortis of Grenchen. The watch only went into production late in the decade, and just a few thousand were produced before the Great Depression soon spelled the end.

You might also enjoy reading about “The Backward Evolution of the Rotating Bezel“

Harwood showed that the advent of the wristwatch had created customer demand for a self-winding movement, and the race was on to deliver a more practical one. I previously wrote about Eugène Meylan’s automatic winding mechanism, which was sold by Glycine starting in 1931. Another early player in automatic watches was Blancpain, which built a patented sliding watch called the Rolls for the French firm, Léon Hatot. Another modestly-successful automatic watch in this period was the Wig-Wag, which used the motion of the movement relative to the strap to wind the watch. But these oddball automatics soon fell by the wayside3.

It was the Rolex Oyster Perpetual that brought together all of the elements of the modern automatic wristwatch. Introduced about 19344, Rolex used a centrally-mounted rotor and winding mechanism stacked on top of their excellent movement. This technique was impractical in a pocket watch (which tended to sit vertically in a pocket) but made much more sense when strapped to a wrist. But the Rolex Oyster Perpetual movement was so thick it had to be mounted in a so-called “bubble-back” expanded case.

Seeing their success, especially though World War II, every Swiss company was racing to compete with Rolex with their own waterproof automatic watch. Felsa’s 1947 Bidynator brought bi-directional winding to the table5, ETA’s 1948 Eternamatic showed the potential of a rotor supported by ball bearings6, and Patek Philippe developed a “circumferential” rotor that extended down and around the movement. But all of these mechanisms added thickness, even as stylish consumers of the 1950s demanded ever-thinner watches. But making a thin automatic watch was inconceivable until the late 1950s, and the slimmest offerings (Zenith’s Cal. 133 and Movado’s Cal. 331) were bumper automatic movements, thin by accident rather than intentional design.

Hans Kocher and the Micro-Rotor

Hans Kocher grew up in the shadow of the H. Williamson watch factory in Büren an der Aare, Switzerland. He ran errands for the company as a young boy, and his work ethic so impressed the company’s chairman that he was sent to London to learn the business. But Kocher’s life took a turn when he met Austrian-born Josefine Rinner, a confectionary entrepreneur living in Zürich. The couple moved to Spain after the war, and their son (also named Hans) was born there in 1919. Kocher only settled down in 1923, marrying Josefine and returning to Bienne to work for the Williamson company. But the factory was bankrupt by 1931, with a group of local businessmen purchasing it. They invited Hans Kocher to return to Büren to take over management of the factory in 1932, and he spent the rest of his career there.

But this is the story of the younger Hans Kocher, who apprenticed in Büren before studying at the Technical school in Bienne. Following World War II, young Hans Kocher moved to Saint-Imier and worked in the technical department of the nearby Cortébert Watch Company. He was a wunderkind, filing patents, developing a central-seconds movement, and reorganizing the company’s manufacturing process. In 1951, after he proved himself, Kocher returned home to become technical director of the Buren Watch Company7.

Kocher believed that technology could elevate Buren in the competitive Swiss watch market and decided to build the best-possible automatic watch movement. Although many aspects of automatic winding were already patented by others, he saw an opportunity to address some of the shortcomings of contemporary automatic watches. For example, Kocher invented a mechanism to allow an automatic watch to be wound by hand, addressing widespread anxiety about power reserve. He also invented a few different bi-directional winding mechanisms and a more effective jewel pivot.

Another Kocher invention seemed to go nowhere: He embedded a tiny rotor inside the main winding rotor, creating a “Tilt-A-Whirl” effect to accelerate startup. Although this didn’t make it into production, this was the first glimpse of a micro-rotor winding system. A month later, Kocher filed a patent that he would later call his greatest work.

On June 21, 1954, Buren Watch Company filed a patent for a fully-realized micro-rotor automatic watch movement. Rather than adding a rotor on top of an existing movement, Hans Kocher redesigned the entire ebauche, reorganizing the wheel train to sink a tiny rotor inside. This was much more than a re-packaging effort, with nearly every component re-designed.

It would take nearly four years of development to bring the micro-rotor movement to market. The Swiss government had largely restricted companies from producing their own ebauches, but this was allowed for in-house and complicated movements. And the micro-rotor was indeed a very complicated movement, requiring entirely new design and tooling to be installed at the factory in Büren!

Kocher’s original micro-rotor movement design was elegant and symmetrical, already quite well-developed even in 1954. He called it a “planetary rotor” because he thought it resembled the planetary gearsets in automatic transmissions. But he spent years working on the construction and mechanics of the rotor and the exact arrangement of the wheels and bridges. And he soon had an unexpected collaborator.

Universal, Froidevaux, and Bandi

On May 27, 1955, Manufacture des Montres Universal of Geneva filed a remarkably similar patent for a micro-rotor movement. This was 11 months after Buren’s filing, yet three years before either patent would be published. Although the Swiss patent is un-signed, the American patent specifies that the inventors were Jean-Michel Froidevaux and Fred Bandi, two technician-watchmakers even younger than Hans Kocher. Both were incredibly talented and had made numerous inventions related to automatic watch winding and other areas of horology.

At a glance, the Universal patent looks very similar to Buren’s, but a closer examination shows that nearly every aspect of the design is different. The American patent authorities examined it closely, rejecting only the most broad claim made by Universal. Given these differences, and the evident skills and imagination of Froidevaux and Bandi, I believe that it was independently invented.

Froidevaux left Universal by 1956, just as the company was developing the micro-rotor watch movement for production. This was the same year that Universal opened its own new factory near Geneva, severing ties with the chronograph factory in Ponts-de-Martel that had been the source of complicated in-house movements for Universal since 1941. The new Carouge-Genève factory was likely outfitted with new machinery to produce the micro-rotor, along with other in-house movements developed by Fred Bandi.

It is very likely that the amiable Hans Kocher knew of the work underway in Geneva by this time, and he may have offered Fred Bandi some technical advice. Indeed, we know that the two collaborated on a paper outlining the benefits of the micro-rotor movement, which was published in the September/October 1957 edition of Journal Suisse d’Horlogerie. They cite the improvements gained by this design in reducing movement height, stress on the rotor bearings, and ease of servicing.

Up this point the thinnest automatic watch movements (Zénith’s Cal. 133 and Movado’s Cal. 331) had “bumper” movements rather than a free rotor. This is no surprise – the “sandwich stack” required to have a free rotor was inherently thicker than a winding mass that sat on the same plane as the wheel train and balance. But no bumper movement could match a micro-rotor embedded completely into the ebauche. Although not much thinner than hand-winding movements, the Büren and Universal movements were 20% thinner than most automatics at 4.1 to 4.2 mm8.

The Joint Release of the Buren Super Slender and Universal Microtor

On February 18, 1958, Raoul Perret of Universal Genève and Hans Kocher of the Buren Watch Company held a joint press conference in Geneva to announce “the greatest technical advance in 30 years.” Journalists from the major Swiss papers and industry journals learned about the revolutionary new micro-rotor technology, that would enable the companies to deliver the thinnest self-winding watches in the world. The companies promised that new watches using these movements would be released at the Basel Fair in April.

Ten days before the fair, on April 2, 1958, the Swiss paper Neue Zürcher Zeitung published an article with more detail on the technology of these new movements. Noting that “the fundamental concept behind this novel winding mechanism is identical in both designs,” the article praises both companies’ products, noting that “the specific technical solutions employed differ significantly.” This article was written by Fred Bandi, Technical Director for Universal Genève. Hans Kocher also wrote articles about the two companies’ launches, both independently and jointly with Bandi.

Finally, on April 12, 1958, the Basel Fair opened, with both companies showcasing watches housing their new micro-rotor movements. They even placed a joint advertisement in the Journal Suisse d’Horlogerie, featuring the logos of both companies.

The Buren Watch Company showed off their new Super Slender watch line at the fair, featuring Cal. 1000. This was a new ultra-thin watch line with a case meant to make the most of their “thinnest-ever” automatic watch movement. Confusingly, the company’s Basel Fair booth was a generic paean to post-war globalization, dedicated to the theme “l’universalité.” The new Super Slender movement was depicted on a small card at the corner, with the ultra-thin watches arranged among other more mundane products.

Universal Genève presented a strong contrast, dedicating their entire display to the new Microtor movement. They even built a large model in a transparent plexiglass case, demonstrating the internal relationship between the micro-rotor and wheel train. The new Cal. 215 was used in an existing product line, the Polerouter (which had been introduced as “Polarouter” in 1954). Although Universal offered new dial designs for 1958, the Microtor’s slimmer profile was not leveraged for a watch that was notably thin.

Both watches were brought to market in the following months with no hint of production delays. They are widely seen and advertised over the next few years in press coverage, company advertising, and retail promotion. For example, an April 1958 ad for international retailer Turler lists the Universal Polerouter Microtor for 270 francs in steel or 820 francs in gold. Meanwhile, the Buren Super Slender was advertised in 1959 for 170 francs in steel or 185 francs for the model with a calendar complication, called Cal. 1001.

What Happened Next

Buren and Universal leaned heavily into their micro-rotor watch movements for the next few years, developing and updating them continually. And two more ultra-thin automatic movements appeared at Basel in 1959 and 1960: The Sandoz 333, which used a peripheral rotor movement designed by FHF, and Piaget’s knock-out 2.3 mm thin micro-rotor Cal. 12 P. But the introduction of the Bulova Accutron on October 25, 1960 upended the entire industry.

Buren actually introduced two micro-rotor movements at Basel in 1958: The base Cal. 1000 was truly “super slender” at 4.2 mm, but they also showed Cal. 1001, which added a date complication and 0.6 mm thickness. Although not as revolutionary as the micro-rotor, Paul Marmier’s patented date mechanism was quite innovative. It used an eccentric cam to keep the advance finger safely back from the date wheel teeth to avoid the risk of damage. The date advanced in just 12 minutes at midnight, and the mechanism also allowed quicker setting of the date by moving the time back to 11:30.

By 1959 Buren added Cal. 1002 and 1003, which featured a thinner balance cock to make way for an elongated wheel train bridge screwed to the base plate for greater stability. The original Cal. 1000 and 1001 remained in production, however, into the 1960s.

Universal added a date complication as well, though theirs added over 1 mm to the thickness of the base Cal. 215. This did not pose an issue because the Microtor was used in watches of more ordinary thickness like the Polerouter Date. But the Geneva company did finally lean into the thin profile of the basic Microtor movement with the new 1959 Polerouter Jet, boasting that it was as thin as a hand-winding watch and the thinnest waterproof automatic watch in the world. Universal put the Microtor-Calendrier movement on a diet over the next few years, beveling the edges and slimming it to 4.7 mm (once again 0.1 mm thinner than the competing Buren movement). And Universal proved the robustness of their movement by equipping members of the Swiss Greenland Expedition with Microtor-powered Polerouters during the International Geophysical Year.

Other watches had previously been advertised for their ultra-thin profile, including Omega’s Centenaire and Cyma’s Navystar, but Movado, Sandoz, and Piaget were the strongest contenders. Movado had claimed the crown for the thinnest watch in 1935 with the Novoplan and delivered the automatic Cal. 331 in 1952, which was just 4.3 mm thick thanks to a beveled bumper rotor.

Sandoz announced the “thinnest waterproof watch” in 1954 with their hand-winding Cal. 55, allowing them to produce a 6.9 mm watch. And they saw an opportunity in a peripheral rotor concept under development at the Fabrique d’Horlogerie de Fontainemelon. Unaware of the micro-rotor8, Sandoz and FHF targeted the 1959 Basel Fair to launch this new ultra-thin automatic watch. Despite being upstaged, the Sandoz 333 remains the first peripheral-winding automatic watch to market.

Piaget claimed outright victory for the thinnest watch in 1957 with the 4 mm Ref. 904, housing the 2.0 mm Cal. 9 P. Valentin Piaget of their specialist movement maker Complications SA saw unrealized potential in the micro-rotor concept. His Cal. 12 P, patented in 1958 and announced at the Basel Fair in 1960, dispensed with the center wheel and radically sliced away the ebauche. Measuring just 2.3 mm thick, this movement allowed Piaget’s Ref. 12 watches to stay at just 4 mm thick overall. Piaget has remained committed to this design, producing Cal. 1200 to this day!

Buren embraced Piaget’s ideas, and their Cal. 1280 was similarly stripped-down, coming in at just 2.85 mm thick. This was used in their modern Intra Matic9 line, launched at the Basel Fair in 1965. Variations with date and central seconds ranged up to 3.60 mm, still over half a millimeter thinner than their original Super Slender.

The Intramatic movement made history on March 3, 1969 when Hans Kocher10 and Gerald Dubois announced the Chronomatic movement, built on Buren’s micro-rotor ebauche. This would be the first Swiss automatic chronograph in customer hands, used by Breitling, Heuer, and Hamilton, which had purchased Buren in February of 1966. Hamilton-Buren was taken over by the SIHH group in 1971 and the once-great Büren factory was closed the following year, with all assets sold. This came just as the Chronomatic was gaining market traction and sadly just before the launch of Buren’s great Calbre 8211.

Universal also collaborated with Piaget, filing a joint patent in March of 1959 for a slim ratcheting winding system for micro-rotor movements. They continually updated their Microtor movement line, culminating in the 1966 introduction of the re-designed Cal. 66. Unlike the hand-made Piaget Cal. 12 P, the new Universal and Buren movements were designed for mass production and daily wear. And Universal once again beat Buren’s mark, with their ebauche measuring just 2.50 mm thick. This time Universal leaned into the thinness of the movement, matching Piaget with a new Golden Shadow watch line just 4 mm thick.

Everything changed for Universal in August of 1966, as the Bulova Watch Company of New York purchased the company. Flush with cash from the Accutron, a global phenomenon never before seen in watchmaking, Bulova sought to solidify its control over the luxury watch industry by bringing the Geneva firm under its control. Universal continued production of the Microtor family into the 1970s and even developed the world’s thinnest quartz movement in 197512. But Bulova was slow to embrace quartz as the market for the Accutron evaporated. The Universal factory in Geneva was bankrupt by the late 1970s and was sold in 1983 to new investors.

The Micro-Rotor Lives On

The micro-rotor is not dead. Far from it: There are more micro-rotor movements on the market today than ever before!

Patek Philippe filed for a patent their own micro-rotor movement in 1975, bringing their Cal. 240 to market a few years later. It has been continually updated and is one of the most-loved movements by enthusiasts like me. Chopard Manufacture leaned into the micro-rotor concept with the launch of the L.U.C movements in 1997, and it remains a highlight of the company’s offerings. A new Universal Genève launched in 2005, bringing a new Microtor (Cal. UG-100) to market in 2006. Schwarz Etienne and Parmigiani Fleurier both introduced new micro-rotor movements in 2010, and both supply these to other fine watch makers to this day. Armin Strom, Hermès, Girard-Perregaux, Bulgari, and many others have also released high-end micro-rotor movements. And Piaget never stopped developing their micro-rotor movements.

Universal was re-launched as an upscale sister brand to Breitling on April 8, 2026 and two new Microtor movements form the core of the new offerings. The new Polerouter Microtor is the first double-barrel micro-rotor movement I know of, and is a lovely tribute to Hans Kocher, who was deeply involved in both innovations. And the new Compax Microtor movement recalls the pioneering Chronomatic movement.

Research Notes

1. The question of whether Perrelet was the first to create a self-winding watch was a matter of great interest through the 20th century. Historian Alfred Chapuis uncovered many prior and subsequent designs, yet he concluded in his seminal book “La Montre Automatique Ancienne” that Perrelet absolutely deserved the credit. That being said, the self-winding watch “discovered” by Léon Leroy of Paris in 1949 may not have been created by Perrelet, according to a 1996 Europa Star article by Jean-Claude Nicolet with rebuttal by Jean-Claude Sabrier.
2. Not being a watch industry insider, Harwood may have been completely unaware that dozens of watchmakers had developed self-winding watches for over a century prior to his invention. And L. Leroy of Paris had already produced a self-winding wristwatch a year before Harwood’s patent. But he was the first to recognize the market for a wristwatch with a sealed case and self-winding movement.
3. The sliding weight concept was actually successfully revived by Pierce just after World War II. This “dissident” Moutier firm was unwilling to abide by the Swiss cartel’s production quotas, so they were blocked from working with nearly every other company. So they developed their own slim sliding-weight automatic, an amazing in-house chronograph movement, and more! In modern times we have seen another sliding-weight automatic, the Corum Golden Bridge Automatic.
4. I’m not a Rolex expert, but I am confounded by the lack of definitive history for this most-important watchmaker. The earliest mention I could find of the Oyster Perpetual comes from Journal Suisse d’Horlogerie in September of 1934, and it was fully illustrated in January of 1936. Given that Rolex trademarked the name in 1932, I guess that places the introduction of the Rolex Perpetual movement in 1933 or 1934. It definitely wasn’t 1931, despite countless blog posts and Rolex’s own advertising.
5. Incredibly, some of the earliest known self-winding pocket watch movements also have clever bi-directional winding solutions: The four controversial maybe-Perrelet movements have a pawl winding system similar to the much-later Pellaton and Magic Lever, and many of the “shaker” movements had bi-directional winding too. But Felsa’s elegant Bidynator inspired the whole industry to adopt this concept. Surprisingly, modern movements are dropping bi-directional winding, finding that it’s not actually all that useful.
6. Ball bearing support for a winding rotor was patented in 1929. But these typically placed the bearings at the periphery, supporting the rotor itself. ETA’s original Eternamatic was a tiny movement for ladies watches so the engineers brought the ball bearings to the center. Seeing how well it worked, the “five balls” became the logo of Eterna!
7. I should clarify that the name of the town is “Büren an der Aare” and it is commonly called “Büren”. But the brand name of the watch company, officially adopted by H. Williamson in 1916, was “Buren Watch Company” without the umlaut. This was generally used by the company through the 1960s, though they sometimes did include the umlaut in advertising and public communication. Confusingly, most patents list it using the Anglicized form of the name of the town, “Bueren Watch Company.” I try to be consistent (or perhaps confusing) and use “Büren” to refer to the town and “Buren” to refer to the company.
8. Oops! The Fabrique d’Horlogerie de Fontainemelon was working on another thin automatic winding system at the same time, filing patents on their peripheral rotor on September 11, 1956. This was before the announcement or publication of the micro-rotor, and they no-doubt thought that their “Fontomatic” Cal. 65 would be the thinnest automatic movement at just 4.5 mm. This came to market in 1959 as the Sandoz 333, and advertisements for this latecomer specifically neglect to mention that number, which was surpassed a year earlier by both Buren and Universal.
9. Buren trademarked “Intra Matic” in 1964 and used this name in the 1965 launch. But they also used “Intramatic” in this period, variously using both names. They had a sub-model called the “Intramatic Polestar” or “Intra Matic Pole-Star” in the 1960s as well, and I can’t imagine Universal loved this name.
10. This would be Hans Kocher-Aeschbacher, the son, rather than his father Hans Kocher-Rinner, who retired that same year. The younger Hans Kocher was a truly remarkable man, deserving of a Prix Gaïa award in all three categories: Watchmaker, businessman, and historian. He was also incredibly magnanimous, not giving undue attention in his industry history writing and speaking to the Buren “planetary rotor” despite considering it his life’s greatest work.
11. I’m wearing my Buren Calibre 82 watch as I write this!
12. The 1975 Golden Shadow and White Shadow Quartz movement measured 3.45 mm thick. It was rapidly surpassed by Citizen, just under 1 mm in 1978, Seiko, 0.90 mm that same year, and the incredible Swiss Delirium movements.

The Day the Micro-Rotor Was Introduced: Buren Super Slender and Universal Microtor

On February 18, 1958, representatives from Buren Watch Company and Universal Genève announced “the greatest technical advance in 30 years,” the micro-rotor automatic watch movement. This joint announcement, and the actions of the inventors and companies before and after it, contradict the oft-repeated story of conflict between them. In fact, the invention and introduction was friendly, thanks to the cordial Hans Kocher, who invented the micro-rotor yet allowed others to share the limelight and the credit.

Debunking the Legend

Like so many areas of watchmaking history, the story of the micro-rotor automatic watch is rich with folklore. And like too many other topics, most of those stories are flat-out wrong. I have been hearing this particular story for years, and was shocked to find that it is entirely contradicted by the plain facts published at the time.

Here’s the gist of what I was told about the launch of the Buren and Universal micro-rotor movements:

• Buren was first to market, introducing their micro-rotor movement in 1957 or maybe even 1954
• Universal infringed on Buren’s patent, didn’t have the technical expertise to design a new movement, and maybe never even had a patent of their own
• Buren sued Universal or tried to block them from marketing the Microtor
• And inexplicably that Universal actually produced the Buren movement because they couldn’t get it to work

None of this is remotely true.

• Technician-watchmaker Hans Kocher of Buren Watch Company invented the micro-rotor movement, filing a patent in 1954
• Jean-Michel Froidevaux and Fred Bandi, skilled technician-watchmakers at Universal, independently invented their own micro-rotor technology, filing a patent just 11 months later
• Kocher and Bandi collaborated on the launch, co-authoring an article on the technology and writing about each other’s work in supportive terms
• Buren and Universal announced their work at a joint press conference on February 18, 1958 and released their micro-rotor watches at the Basel Fair that year
• The companies targeted different markets and there is no sign of a lawsuit or any acrimony
• Both companies, along with Piaget, continued actively to develop micro-rotor movement technology for over a decade
• The technology was abandoned after both were purchased by American companies more interested in quartz electronic watches

So let’s sit back and enjoy the true story of the development of the micro-rotor watch movement!

The Rise of Self-Winding Watches

Le Locle watchmaker Abraham-Louis Perrelet is usually credited for building the first self-winding watch in the 1770s. Many1 have questioned the primacy of Perrelet’s “montre à secousses” (“shaking watch”), but many subsequent watchmakers, including Abraham-Louis Breguet, Louis Recordin, and the Jaquet-Droz family, claimed to have been inspired by his design. Perrelet’s watch used a weight mounted to the side of the movement, causing it to shake when moved. The concept of automatic winding (and even the name “perpetual”) were widely known through the 19th century but such a complex mechanism was deemed unnecessary to bring to market.

After World War I, Englishman John Harwood saw a need for self-winding watch. Soldiers were increasingly wearing wristwatches, and these were often damaged by moisture and dust. Inspired by a playground see-saw, Harwood independently2 invented a rocking weight segment that could wind the watch without a hole in the case. He patented the concept in 1923, built a prototype using a Blancpain movement, and brought the Harwood Perpetual to market with the help of A. Schild and Fortis of Grenchen. The watch only went into production late in the decade, and just a few thousand were produced before the Great Depression soon spelled the end.

You might also enjoy reading about “The Backward Evolution of the Rotating Bezel“

Harwood showed that the advent of the wristwatch had created customer demand for a self-winding movement, and the race was on to deliver a more practical one. I previously wrote about Eugène Meylan’s automatic winding mechanism, which was sold by Glycine starting in 1931. Another early player in automatic watches was Blancpain, which built a patented sliding watch called the Rolls for the French firm, Léon Hatot. Another modestly-successful automatic watch in this period was the Wig-Wag, which used the motion of the movement relative to the strap to wind the watch. But these oddball automatics soon fell by the wayside3.

It was the Rolex Oyster Perpetual that brought together all of the elements of the modern automatic wristwatch. Introduced about 19344, Rolex used a centrally-mounted rotor and winding mechanism stacked on top of their excellent movement. This technique was impractical in a pocket watch (which tended to sit vertically in a pocket) but made much more sense when strapped to a wrist. But the Rolex Oyster Perpetual movement was so thick it had to be mounted in a so-called “bubble-back” expanded case.

Seeing their success, especially though World War II, every Swiss company was racing to compete with Rolex with their own waterproof automatic watch. Felsa’s 1947 Bidynator brought bi-directional winding to the table5, ETA’s 1948 Eternamatic showed the potential of a rotor supported by ball bearings6, and Patek Philippe developed a “circumferential” rotor that extended down and around the movement. But all of these mechanisms added thickness, even as stylish consumers of the 1950s demanded ever-thinner watches. But making a thin automatic watch was inconceivable until the late 1950s, and the slimmest offerings (Zenith’s Cal. 133 and Movado’s Cal. 331) were bumper automatic movements, thin by accident rather than intentional design.

Hans Kocher and the Micro-Rotor

Hans Kocher grew up in the shadow of the H. Williamson watch factory in Büren an der Aare, Switzerland. He ran errands for the company as a young boy, and his work ethic so impressed the company’s chairman that he was sent to London to learn the business. But Kocher’s life took a turn when he met Austrian-born Josefine Rinner, a confectionary entrepreneur living in Zürich. The couple moved to Spain after the war, and their son (also named Hans) was born there in 1919. Kocher only settled down in 1923, marrying Josefine and returning to Bienne to work for the Williamson company. But the factory was bankrupt by 1931, with a group of local businessmen purchasing it. They invited Hans Kocher to return to Büren to take over management of the factory in 1932, and he spent the rest of his career there.

But this is the story of the younger Hans Kocher, who apprenticed in Büren before studying at the Technical school in Bienne. Following World War II, young Hans Kocher moved to Saint-Imier and worked in the technical department of the nearby Cortébert Watch Company. He was a wunderkind, filing patents, developing a central-seconds movement, and reorganizing the company’s manufacturing process. In 1951, after he proved himself, Kocher returned home to become technical director of the Buren Watch Company7.

Kocher believed that technology could elevate Buren in the competitive Swiss watch market and decided to build the best-possible automatic watch movement. Although many aspects of automatic winding were already patented by others, he saw an opportunity to address some of the shortcomings of contemporary automatic watches. For example, Kocher invented a mechanism to allow an automatic watch to be wound by hand, addressing widespread anxiety about power reserve. He also invented a few different bi-directional winding mechanisms and a more effective jewel pivot.

Another Kocher invention seemed to go nowhere: He embedded a tiny rotor inside the main winding rotor, creating a “Tilt-A-Whirl” effect to accelerate startup. Although this didn’t make it into production, this was the first glimpse of a micro-rotor winding system. A month later, Kocher filed a patent that he would later call his greatest work.

On June 21, 1954, Buren Watch Company filed a patent for a fully-realized micro-rotor automatic watch movement. Rather than adding a rotor on top of an existing movement, Hans Kocher redesigned the entire ebauche, reorganizing the wheel train to sink a tiny rotor inside. This was much more than a re-packaging effort, with nearly every component re-designed.

It would take nearly four years of development to bring the micro-rotor movement to market. The Swiss government had largely restricted companies from producing their own ebauches, but this was allowed for in-house and complicated movements. And the micro-rotor was indeed a very complicated movement, requiring entirely new design and tooling to be installed at the factory in Büren!

Kocher’s original micro-rotor movement design was elegant and symmetrical, already quite well-developed even in 1954. He called it a “planetary rotor” because he thought it resembled the planetary gearsets in automatic transmissions. But he spent years working on the construction and mechanics of the rotor and the exact arrangement of the wheels and bridges. And he soon had an unexpected collaborator.

Universal, Froidevaux, and Bandi

On May 27, 1955, Manufacture des Montres Universal of Geneva filed a remarkably similar patent for a micro-rotor movement. This was 11 months after Buren’s filing, yet three years before either patent would be published. Although the Swiss patent is un-signed, the American patent specifies that the inventors were Jean-Michel Froidevaux and Fred Bandi, two technician-watchmakers even younger than Hans Kocher. Both were incredibly talented and had made numerous inventions related to automatic watch winding and other areas of horology.

At a glance, the Universal patent looks very similar to Buren’s, but a closer examination shows that nearly every aspect of the design is different. The American patent authorities examined it closely, rejecting only the most broad claim made by Universal. Given these differences, and the evident skills and imagination of Froidevaux and Bandi, I believe that it was independently invented.

Froidevaux left Universal by 1956, just as the company was developing the micro-rotor watch movement for production. This was the same year that Universal opened its own new factory near Geneva, severing ties with the chronograph factory in Ponts-de-Martel that had been the source of complicated in-house movements for Universal since 1941. The new Carouge-Genève factory was likely outfitted with new machinery to produce the micro-rotor, along with other in-house movements developed by Fred Bandi.

It is very likely that the amiable Hans Kocher knew of the work underway in Geneva by this time, and he may have offered Fred Bandi some technical advice. Indeed, we know that the two collaborated on a paper outlining the benefits of the micro-rotor movement, which was published in the September/October 1957 edition of Journal Suisse d’Horlogerie. They cite the improvements gained by this design in reducing movement height, stress on the rotor bearings, and ease of servicing.

Up this point the thinnest automatic watch movements (Zénith’s Cal. 133 and Movado’s Cal. 331) had “bumper” movements rather than a free rotor. This is no surprise – the “sandwich stack” required to have a free rotor was inherently thicker than a winding mass that sat on the same plane as the wheel train and balance. But no bumper movement could match a micro-rotor embedded completely into the ebauche. Although not much thinner than hand-winding movements, the Büren and Universal movements were 20% thinner than most automatics at 4.1 to 4.2 mm8.

The Joint Release of the Buren Super Slender and Universal Microtor

On February 18, 1958, Raoul Perret of Universal Genève and Hans Kocher of the Buren Watch Company held a joint press conference in Geneva to announce “the greatest technical advance in 30 years.” Journalists from the major Swiss papers and industry journals learned about the revolutionary new micro-rotor technology, that would enable the companies to deliver the thinnest self-winding watches in the world. The companies promised that new watches using these movements would be released at the Basel Fair in April.

Ten days before the fair, on April 2, 1958, the Swiss paper Neue Zürcher Zeitung published an article with more detail on the technology of these new movements. Noting that “the fundamental concept behind this novel winding mechanism is identical in both designs,” the article praises both companies’ products, noting that “the specific technical solutions employed differ significantly.” This article was written by Fred Bandi, Technical Director for Universal Genève. Hans Kocher also wrote articles about the two companies’ launches, both independently and jointly with Bandi.

Finally, on April 12, 1958, the Basel Fair opened, with both companies showcasing watches housing their new micro-rotor movements. They even placed a joint advertisement in the Journal Suisse d’Horlogerie, featuring the logos of both companies.

The Buren Watch Company showed off their new Super Slender watch line at the fair, featuring Cal. 1000. This was a new ultra-thin watch line with a case meant to make the most of their “thinnest-ever” automatic watch movement. Confusingly, the company’s Basel Fair booth was a generic paean to post-war globalization, dedicated to the theme “l’universalité.” The new Super Slender movement was depicted on a small card at the corner, with the ultra-thin watches arranged among other more mundane products.

Universal Genève presented a strong contrast, dedicating their entire display to the new Microtor movement. They even built a large model in a transparent plexiglass case, demonstrating the internal relationship between the micro-rotor and wheel train. The new Cal. 215 was used in an existing product line, the Polerouter (which had been introduced as “Polarouter” in 1954). Although Universal offered new dial designs for 1958, the Microtor’s slimmer profile was not leveraged for a watch that was notably thin.

Both watches were brought to market in the following months with no hint of production delays. They are widely seen and advertised over the next few years in press coverage, company advertising, and retail promotion. For example, an April 1958 ad for international retailer Turler lists the Universal Polerouter Microtor for 270 francs in steel or 820 francs in gold. Meanwhile, the Buren Super Slender was advertised in 1959 for 170 francs in steel or 185 francs for the model with a calendar complication, called Cal. 1001.

What Happened Next

Buren and Universal leaned heavily into their micro-rotor watch movements for the next few years, developing and updating them continually. And two more ultra-thin automatic movements appeared at Basel in 1959 and 1960: The Sandoz 333, which used a peripheral rotor movement designed by FHF, and Piaget’s knock-out 2.3 mm thin micro-rotor Cal. 12 P. But the introduction of the Bulova Accutron on October 25, 1960 upended the entire industry.

Buren actually introduced two micro-rotor movements at Basel in 1958: The base Cal. 1000 was truly “super slender” at 4.2 mm, but they also showed Cal. 1001, which added a date complication and 0.6 mm thickness. Although not as revolutionary as the micro-rotor, Paul Marmier’s patented date mechanism was quite innovative. It used an eccentric cam to keep the advance finger safely back from the date wheel teeth to avoid the risk of damage. The date advanced in just 12 minutes at midnight, and the mechanism also allowed quicker setting of the date by moving the time back to 11:30.

By 1959 Buren added Cal. 1002 and 1003, which featured a thinner balance cock to make way for an elongated wheel train bridge screwed to the base plate for greater stability. The original Cal. 1000 and 1001 remained in production, however, into the 1960s.

Universal added a date complication as well, though theirs added over 1 mm to the thickness of the base Cal. 215. This did not pose an issue because the Microtor was used in watches of more ordinary thickness like the Polerouter Date. But the Geneva company did finally lean into the thin profile of the basic Microtor movement with the new 1959 Polerouter Jet, boasting that it was as thin as a hand-winding watch and the thinnest waterproof automatic watch in the world. Universal put the Microtor-Calendrier movement on a diet over the next few years, beveling the edges and slimming it to 4.7 mm (once again 0.1 mm thinner than the competing Buren movement). And Universal proved the robustness of their movement by equipping members of the Swiss Greenland Expedition with Microtor-powered Polerouters during the International Geophysical Year.

Other watches had previously been advertised for their ultra-thin profile, including Omega’s Centenaire and Cyma’s Navystar, but Movado, Sandoz, and Piaget were the strongest contenders. Movado had claimed the crown for the thinnest watch in 1935 with the Novoplan and delivered the automatic Cal. 331 in 1952, which was just 4.3 mm thick thanks to a beveled bumper rotor.

Sandoz announced the “thinnest waterproof watch” in 1954 with their hand-winding Cal. 55, allowing them to produce a 6.9 mm watch. And they saw an opportunity in a peripheral rotor concept under development at the Fabrique d’Horlogerie de Fontainemelon. Unaware of the micro-rotor8, Sandoz and FHF targeted the 1959 Basel Fair to launch this new ultra-thin automatic watch. Despite being upstaged, the Sandoz 333 remains the first peripheral-winding automatic watch to market.

Piaget claimed outright victory for the thinnest watch in 1957 with the 4 mm Ref. 904, housing the 2.0 mm Cal. 9 P. Valentin Piaget of their specialist movement maker Complications SA saw unrealized potential in the micro-rotor concept. His Cal. 12 P, patented in 1958 and announced at the Basel Fair in 1960, dispensed with the center wheel and radically sliced away the ebauche. Measuring just 2.3 mm thick, this movement allowed Piaget’s Ref. 12 watches to stay at just 4 mm thick overall. Piaget has remained committed to this design, producing Cal. 1200 to this day!

Buren embraced Piaget’s ideas, and their Cal. 1280 was similarly stripped-down, coming in at just 2.85 mm thick. This was used in their modern Intra Matic9 line, launched at the Basel Fair in 1965. Variations with date and central seconds ranged up to 3.60 mm, still over half a millimeter thinner than their original Super Slender.

The Intramatic movement made history on March 3, 1969 when Hans Kocher10 and Gerald Dubois announced the Chronomatic movement, built on Buren’s micro-rotor ebauche. This would be the first Swiss automatic chronograph in customer hands, used by Breitling, Heuer, and Hamilton, which had purchased Buren in February of 1966. Hamilton-Buren was taken over by the SIHH group in 1971 and the once-great Büren factory was closed the following year, with all assets sold. This came just as the Chronomatic was gaining market traction and sadly just before the launch of Buren’s great Calbre 8211.

Universal also collaborated with Piaget, filing a joint patent in March of 1959 for a slim ratcheting winding system for micro-rotor movements. They continually updated their Microtor movement line, culminating in the 1966 introduction of the re-designed Cal. 66. Unlike the hand-made Piaget Cal. 12 P, the new Universal and Buren movements were designed for mass production and daily wear. And Universal once again beat Buren’s mark, with their ebauche measuring just 2.50 mm thick. This time Universal leaned into the thinness of the movement, matching Piaget with a new Golden Shadow watch line just 4 mm thick.

Everything changed for Universal in August of 1966, as the Bulova Watch Company of New York purchased the company. Flush with cash from the Accutron, a global phenomenon never before seen in watchmaking, Bulova sought to solidify its control over the luxury watch industry by bringing the Geneva firm under its control. Universal continued production of the Microtor family into the 1970s and even developed the world’s thinnest quartz movement in 197512. But Bulova was slow to embrace quartz as the market for the Accutron evaporated. The Universal factory in Geneva was bankrupt by the late 1970s and was sold in 1983 to new investors.

The Micro-Rotor Lives On

The micro-rotor is not dead. Far from it: There are more micro-rotor movements on the market today than ever before!

Patek Philippe filed for a patent their own micro-rotor movement in 1975, bringing their Cal. 240 to market a few years later. It has been continually updated and is one of the most-loved movements by enthusiasts like me. Chopard Manufacture leaned into the micro-rotor concept with the launch of the L.U.C movements in 1997, and it remains a highlight of the company’s offerings. A new Universal Genève launched in 2005, bringing a new Microtor (Cal. UG-100) to market in 2006. Schwarz Etienne and Parmigiani Fleurier both introduced new micro-rotor movements in 2010, and both supply these to other fine watch makers to this day. Armin Strom, Hermès, Girard-Perregaux, Bulgari, and many others have also released high-end micro-rotor movements. And Piaget never stopped developing their micro-rotor movements.

Universal was re-launched as an upscale sister brand to Breitling on April 8, 2026 and two new Microtor movements form the core of the new offerings. The new Polerouter Microtor is the first double-barrel micro-rotor movement I know of, and is a lovely tribute to Hans Kocher, who was deeply involved in both innovations. And the new Compax Microtor movement recalls the pioneering Chronomatic movement.

Research Notes

1. The question of whether Perrelet was the first to create a self-winding watch was a matter of great interest through the 20th century. Historian Alfred Chapuis uncovered many prior and subsequent designs, yet he concluded in his seminal book “La Montre Automatique Ancienne” that Perrelet absolutely deserved the credit. That being said, the self-winding watch “discovered” by Léon Leroy of Paris in 1949 may not have been created by Perrelet, according to a 1996 Europa Star article by Jean-Claude Nicolet with rebuttal by Jean-Claude Sabrier.
2. Not being a watch industry insider, Harwood may have been completely unaware that dozens of watchmakers had developed self-winding watches for over a century prior to his invention. And L. Leroy of Paris had already produced a self-winding wristwatch a year before Harwood’s patent. But he was the first to recognize the market for a wristwatch with a sealed case and self-winding movement.
3. The sliding weight concept was actually successfully revived by Pierce just after World War II. This “dissident” Moutier firm was unwilling to abide by the Swiss cartel’s production quotas, so they were blocked from working with nearly every other company. So they developed their own slim sliding-weight automatic, an amazing in-house chronograph movement, and more! In modern times we have seen another sliding-weight automatic, the Corum Golden Bridge Automatic.
4. I’m not a Rolex expert, but I am confounded by the lack of definitive history for this most-important watchmaker. The earliest mention I could find of the Oyster Perpetual comes from Journal Suisse d’Horlogerie in September of 1934, and it was fully illustrated in January of 1936. Given that Rolex trademarked the name in 1932, I guess that places the introduction of the Rolex Perpetual movement in 1933 or 1934. It definitely wasn’t 1931, despite countless blog posts and Rolex’s own advertising.
5. Incredibly, some of the earliest known self-winding pocket watch movements also have clever bi-directional winding solutions: The four controversial maybe-Perrelet movements have a pawl winding system similar to the much-later Pellaton and Magic Lever, and many of the “shaker” movements had bi-directional winding too. But Felsa’s elegant Bidynator inspired the whole industry to adopt this concept. Surprisingly, modern movements are dropping bi-directional winding, finding that it’s not actually all that useful.
6. Ball bearing support for a winding rotor was patented in 1929. But these typically placed the bearings at the periphery, supporting the rotor itself. ETA’s original Eternamatic was a tiny movement for ladies watches so the engineers brought the ball bearings to the center. Seeing how well it worked, the “five balls” became the logo of Eterna!
7. I should clarify that the name of the town is “Büren an der Aare” and it is commonly called “Büren”. But the brand name of the watch company, officially adopted by H. Williamson in 1916, was “Buren Watch Company” without the umlaut. This was generally used by the company through the 1960s, though they sometimes did include the umlaut in advertising and public communication. Confusingly, most patents list it using the Anglicized form of the name of the town, “Bueren Watch Company.” I try to be consistent (or perhaps confusing) and use “Büren” to refer to the town and “Buren” to refer to the company.
8. Oops! The Fabrique d’Horlogerie de Fontainemelon was working on another thin automatic winding system at the same time, filing patents on their peripheral rotor on September 11, 1956. This was before the announcement or publication of the micro-rotor, and they no-doubt thought that their “Fontomatic” Cal. 65 would be the thinnest automatic movement at just 4.5 mm. This came to market in 1959 as the Sandoz 333, and advertisements for this latecomer specifically neglect to mention that number, which was surpassed a year earlier by both Buren and Universal.
9. Buren trademarked “Intra Matic” in 1964 and used this name in the 1965 launch. But they also used “Intramatic” in this period, variously using both names. They had a sub-model called the “Intramatic Polestar” or “Intra Matic Pole-Star” in the 1960s as well, and I can’t imagine Universal loved this name.
10. This would be Hans Kocher-Aeschbacher, the son, rather than his father Hans Kocher-Rinner, who retired that same year. The younger Hans Kocher was a truly remarkable man, deserving of a Prix Gaïa award in all three categories: Watchmaker, businessman, and historian. He was also incredibly magnanimous, not giving undue attention in his industry history writing and speaking to the Buren “planetary rotor” despite considering it his life’s greatest work.
11. I’m wearing my Buren Calibre 82 watch as I write this!
12. The 1975 Golden Shadow and White Shadow Quartz movement measured 3.45 mm thick. It was rapidly surpassed by Citizen, just under 1 mm in 1978, Seiko, 0.90 mm that same year, and the incredible Swiss Delirium movements.

The Day the Micro-Rotor Was Introduced: Buren Super Slender and Universal Microtor

On February 18, 1958, representatives from Buren Watch Company and Universal Genève announced “the greatest technical advance in 30 years,” the micro-rotor automatic watch movement. This joint announcement, and the actions of the inventors and companies before and after it, contradict the oft-repeated story of conflict between them. In fact, the invention and introduction was friendly, thanks to the cordial Hans Kocher, who invented the micro-rotor yet allowed others to share the limelight and the credit.

Debunking the Legend

Like so many areas of watchmaking history, the story of the micro-rotor automatic watch is rich with folklore. And like too many other topics, most of those stories are flat-out wrong. I have been hearing this particular story for years, and was shocked to find that it is entirely contradicted by the plain facts published at the time.

Here’s the gist of what I was told about the launch of the Buren and Universal micro-rotor movements:

• Buren was first to market, introducing their micro-rotor movement in 1957 or maybe even 1954
• Universal infringed on Buren’s patent, didn’t have the technical expertise to design a new movement, and maybe never even had a patent of their own
• Buren sued Universal or tried to block them from marketing the Microtor
• And inexplicably that Universal actually produced the Buren movement because they couldn’t get it to work

None of this is remotely true.

• Technician-watchmaker Hans Kocher of Buren Watch Company invented the micro-rotor movement, filing a patent in 1954
• Jean-Michel Froidevaux and Fred Bandi, skilled technician-watchmakers at Universal, independently invented their own micro-rotor technology, filing a patent just 11 months later
• Kocher and Bandi collaborated on the launch, co-authoring an article on the technology and writing about each other’s work in supportive terms
• Buren and Universal announced their work at a joint press conference on February 18, 1958 and released their micro-rotor watches at the Basel Fair that year
• The companies targeted different markets and there is no sign of a lawsuit or any acrimony
• Both companies, along with Piaget, continued actively to develop micro-rotor movement technology for over a decade
• The technology was abandoned after both were purchased by American companies more interested in quartz electronic watches

So let’s sit back and enjoy the true story of the development of the micro-rotor watch movement!

The Rise of Self-Winding Watches

Le Locle watchmaker Abraham-Louis Perrelet is usually credited for building the first self-winding watch in the 1770s. Many1 have questioned the primacy of Perrelet’s “montre à secousses” (“shaking watch”), but many subsequent watchmakers, including Abraham-Louis Breguet, Louis Recordin, and the Jaquet-Droz family, claimed to have been inspired by his design. Perrelet’s watch used a weight mounted to the side of the movement, causing it to shake when moved. The concept of automatic winding (and even the name “perpetual”) were widely known through the 19th century but such a complex mechanism was deemed unnecessary to bring to market.

After World War I, Englishman John Harwood saw a need for self-winding watch. Soldiers were increasingly wearing wristwatches, and these were often damaged by moisture and dust. Inspired by a playground see-saw, Harwood independently2 invented a rocking weight segment that could wind the watch without a hole in the case. He patented the concept in 1923, built a prototype using a Blancpain movement, and brought the Harwood Perpetual to market with the help of A. Schild and Fortis of Grenchen. The watch only went into production late in the decade, and just a few thousand were produced before the Great Depression soon spelled the end.

You might also enjoy reading about “The Backward Evolution of the Rotating Bezel“

Harwood showed that the advent of the wristwatch had created customer demand for a self-winding movement, and the race was on to deliver a more practical one. I previously wrote about Eugène Meylan’s automatic winding mechanism, which was sold by Glycine starting in 1931. Another early player in automatic watches was Blancpain, which built a patented sliding watch called the Rolls for the French firm, Léon Hatot. Another modestly-successful automatic watch in this period was the Wig-Wag, which used the motion of the movement relative to the strap to wind the watch. But these oddball automatics soon fell by the wayside3.

It was the Rolex Oyster Perpetual that brought together all of the elements of the modern automatic wristwatch. Introduced about 19344, Rolex used a centrally-mounted rotor and winding mechanism stacked on top of their excellent movement. This technique was impractical in a pocket watch (which tended to sit vertically in a pocket) but made much more sense when strapped to a wrist. But the Rolex Oyster Perpetual movement was so thick it had to be mounted in a so-called “bubble-back” expanded case.

Seeing their success, especially though World War II, every Swiss company was racing to compete with Rolex with their own waterproof automatic watch. Felsa’s 1947 Bidynator brought bi-directional winding to the table5, ETA’s 1948 Eternamatic showed the potential of a rotor supported by ball bearings6, and Patek Philippe developed a “circumferential” rotor that extended down and around the movement. But all of these mechanisms added thickness, even as stylish consumers of the 1950s demanded ever-thinner watches. But making a thin automatic watch was inconceivable until the late 1950s, and the slimmest offerings (Zenith’s Cal. 133 and Movado’s Cal. 331) were bumper automatic movements, thin by accident rather than intentional design.

Hans Kocher and the Micro-Rotor

Hans Kocher grew up in the shadow of the H. Williamson watch factory in Büren an der Aare, Switzerland. He ran errands for the company as a young boy, and his work ethic so impressed the company’s chairman that he was sent to London to learn the business. But Kocher’s life took a turn when he met Austrian-born Josefine Rinner, a confectionary entrepreneur living in Zürich. The couple moved to Spain after the war, and their son (also named Hans) was born there in 1919. Kocher only settled down in 1923, marrying Josefine and returning to Bienne to work for the Williamson company. But the factory was bankrupt by 1931, with a group of local businessmen purchasing it. They invited Hans Kocher to return to Büren to take over management of the factory in 1932, and he spent the rest of his career there.

But this is the story of the younger Hans Kocher, who apprenticed in Büren before studying at the Technical school in Bienne. Following World War II, young Hans Kocher moved to Saint-Imier and worked in the technical department of the nearby Cortébert Watch Company. He was a wunderkind, filing patents, developing a central-seconds movement, and reorganizing the company’s manufacturing process. In 1951, after he proved himself, Kocher returned home to become technical director of the Buren Watch Company7.

Kocher believed that technology could elevate Buren in the competitive Swiss watch market and decided to build the best-possible automatic watch movement. Although many aspects of automatic winding were already patented by others, he saw an opportunity to address some of the shortcomings of contemporary automatic watches. For example, Kocher invented a mechanism to allow an automatic watch to be wound by hand, addressing widespread anxiety about power reserve. He also invented a few different bi-directional winding mechanisms and a more effective jewel pivot.

Another Kocher invention seemed to go nowhere: He embedded a tiny rotor inside the main winding rotor, creating a “Tilt-A-Whirl” effect to accelerate startup. Although this didn’t make it into production, this was the first glimpse of a micro-rotor winding system. A month later, Kocher filed a patent that he would later call his greatest work.

On June 21, 1954, Buren Watch Company filed a patent for a fully-realized micro-rotor automatic watch movement. Rather than adding a rotor on top of an existing movement, Hans Kocher redesigned the entire ebauche, reorganizing the wheel train to sink a tiny rotor inside. This was much more than a re-packaging effort, with nearly every component re-designed.

It would take nearly four years of development to bring the micro-rotor movement to market. The Swiss government had largely restricted companies from producing their own ebauches, but this was allowed for in-house and complicated movements. And the micro-rotor was indeed a very complicated movement, requiring entirely new design and tooling to be installed at the factory in Büren!

Kocher’s original micro-rotor movement design was elegant and symmetrical, already quite well-developed even in 1954. He called it a “planetary rotor” because he thought it resembled the planetary gearsets in automatic transmissions. But he spent years working on the construction and mechanics of the rotor and the exact arrangement of the wheels and bridges. And he soon had an unexpected collaborator.

Universal, Froidevaux, and Bandi

On May 27, 1955, Manufacture des Montres Universal of Geneva filed a remarkably similar patent for a micro-rotor movement. This was 11 months after Buren’s filing, yet three years before either patent would be published. Although the Swiss patent is un-signed, the American patent specifies that the inventors were Jean-Michel Froidevaux and Fred Bandi, two technician-watchmakers even younger than Hans Kocher. Both were incredibly talented and had made numerous inventions related to automatic watch winding and other areas of horology.

At a glance, the Universal patent looks very similar to Buren’s, but a closer examination shows that nearly every aspect of the design is different. The American patent authorities examined it closely, rejecting only the most broad claim made by Universal. Given these differences, and the evident skills and imagination of Froidevaux and Bandi, I believe that it was independently invented.

Froidevaux left Universal by 1956, just as the company was developing the micro-rotor watch movement for production. This was the same year that Universal opened its own new factory near Geneva, severing ties with the chronograph factory in Ponts-de-Martel that had been the source of complicated in-house movements for Universal since 1941. The new Carouge-Genève factory was likely outfitted with new machinery to produce the micro-rotor, along with other in-house movements developed by Fred Bandi.

It is very likely that the amiable Hans Kocher knew of the work underway in Geneva by this time, and he may have offered Fred Bandi some technical advice. Indeed, we know that the two collaborated on a paper outlining the benefits of the micro-rotor movement, which was published in the September/October 1957 edition of Journal Suisse d’Horlogerie. They cite the improvements gained by this design in reducing movement height, stress on the rotor bearings, and ease of servicing.

Up this point the thinnest automatic watch movements (Zénith’s Cal. 133 and Movado’s Cal. 331) had “bumper” movements rather than a free rotor. This is no surprise – the “sandwich stack” required to have a free rotor was inherently thicker than a winding mass that sat on the same plane as the wheel train and balance. But no bumper movement could match a micro-rotor embedded completely into the ebauche. Although not much thinner than hand-winding movements, the Büren and Universal movements were 20% thinner than most automatics at 4.1 to 4.2 mm8.

The Joint Release of the Buren Super Slender and Universal Microtor

On February 18, 1958, Raoul Perret of Universal Genève and Hans Kocher of the Buren Watch Company held a joint press conference in Geneva to announce “the greatest technical advance in 30 years.” Journalists from the major Swiss papers and industry journals learned about the revolutionary new micro-rotor technology, that would enable the companies to deliver the thinnest self-winding watches in the world. The companies promised that new watches using these movements would be released at the Basel Fair in April.

Ten days before the fair, on April 2, 1958, the Swiss paper Neue Zürcher Zeitung published an article with more detail on the technology of these new movements. Noting that “the fundamental concept behind this novel winding mechanism is identical in both designs,” the article praises both companies’ products, noting that “the specific technical solutions employed differ significantly.” This article was written by Fred Bandi, Technical Director for Universal Genève. Hans Kocher also wrote articles about the two companies’ launches, both independently and jointly with Bandi.

Finally, on April 12, 1958, the Basel Fair opened, with both companies showcasing watches housing their new micro-rotor movements. They even placed a joint advertisement in the Journal Suisse d’Horlogerie, featuring the logos of both companies.

The Buren Watch Company showed off their new Super Slender watch line at the fair, featuring Cal. 1000. This was a new ultra-thin watch line with a case meant to make the most of their “thinnest-ever” automatic watch movement. Confusingly, the company’s Basel Fair booth was a generic paean to post-war globalization, dedicated to the theme “l’universalité.” The new Super Slender movement was depicted on a small card at the corner, with the ultra-thin watches arranged among other more mundane products.

Universal Genève presented a strong contrast, dedicating their entire display to the new Microtor movement. They even built a large model in a transparent plexiglass case, demonstrating the internal relationship between the micro-rotor and wheel train. The new Cal. 215 was used in an existing product line, the Polerouter (which had been introduced as “Polarouter” in 1954). Although Universal offered new dial designs for 1958, the Microtor’s slimmer profile was not leveraged for a watch that was notably thin.

Both watches were brought to market in the following months with no hint of production delays. They are widely seen and advertised over the next few years in press coverage, company advertising, and retail promotion. For example, an April 1958 ad for international retailer Turler lists the Universal Polerouter Microtor for 270 francs in steel or 820 francs in gold. Meanwhile, the Buren Super Slender was advertised in 1959 for 170 francs in steel or 185 francs for the model with a calendar complication, called Cal. 1001.

What Happened Next

Buren and Universal leaned heavily into their micro-rotor watch movements for the next few years, developing and updating them continually. And two more ultra-thin automatic movements appeared at Basel in 1959 and 1960: The Sandoz 333, which used a peripheral rotor movement designed by FHF, and Piaget’s knock-out 2.3 mm thin micro-rotor Cal. 12 P. But the introduction of the Bulova Accutron on October 25, 1960 upended the entire industry.

Buren actually introduced two micro-rotor movements at Basel in 1958: The base Cal. 1000 was truly “super slender” at 4.2 mm, but they also showed Cal. 1001, which added a date complication and 0.6 mm thickness. Although not as revolutionary as the micro-rotor, Paul Marmier’s patented date mechanism was quite innovative. It used an eccentric cam to keep the advance finger safely back from the date wheel teeth to avoid the risk of damage. The date advanced in just 12 minutes at midnight, and the mechanism also allowed quicker setting of the date by moving the time back to 11:30.

By 1959 Buren added Cal. 1002 and 1003, which featured a thinner balance cock to make way for an elongated wheel train bridge screwed to the base plate for greater stability. The original Cal. 1000 and 1001 remained in production, however, into the 1960s.

Universal added a date complication as well, though theirs added over 1 mm to the thickness of the base Cal. 215. This did not pose an issue because the Microtor was used in watches of more ordinary thickness like the Polerouter Date. But the Geneva company did finally lean into the thin profile of the basic Microtor movement with the new 1959 Polerouter Jet, boasting that it was as thin as a hand-winding watch and the thinnest waterproof automatic watch in the world. Universal put the Microtor-Calendrier movement on a diet over the next few years, beveling the edges and slimming it to 4.7 mm (once again 0.1 mm thinner than the competing Buren movement). And Universal proved the robustness of their movement by equipping members of the Swiss Greenland Expedition with Microtor-powered Polerouters during the International Geophysical Year.

Other watches had previously been advertised for their ultra-thin profile, including Omega’s Centenaire and Cyma’s Navystar, but Movado, Sandoz, and Piaget were the strongest contenders. Movado had claimed the crown for the thinnest watch in 1935 with the Novoplan and delivered the automatic Cal. 331 in 1952, which was just 4.3 mm thick thanks to a beveled bumper rotor.

Sandoz announced the “thinnest waterproof watch” in 1954 with their hand-winding Cal. 55, allowing them to produce a 6.9 mm watch. And they saw an opportunity in a peripheral rotor concept under development at the Fabrique d’Horlogerie de Fontainemelon. Unaware of the micro-rotor8, Sandoz and FHF targeted the 1959 Basel Fair to launch this new ultra-thin automatic watch. Despite being upstaged, the Sandoz 333 remains the first peripheral-winding automatic watch to market.

Piaget claimed outright victory for the thinnest watch in 1957 with the 4 mm Ref. 904, housing the 2.0 mm Cal. 9 P. Valentin Piaget of their specialist movement maker Complications SA saw unrealized potential in the micro-rotor concept. His Cal. 12 P, patented in 1958 and announced at the Basel Fair in 1960, dispensed with the center wheel and radically sliced away the ebauche. Measuring just 2.3 mm thick, this movement allowed Piaget’s Ref. 12 watches to stay at just 4 mm thick overall. Piaget has remained committed to this design, producing Cal. 1200 to this day!

Buren embraced Piaget’s ideas, and their Cal. 1280 was similarly stripped-down, coming in at just 2.85 mm thick. This was used in their modern Intra Matic9 line, launched at the Basel Fair in 1965. Variations with date and central seconds ranged up to 3.60 mm, still over half a millimeter thinner than their original Super Slender.

The Intramatic movement made history on March 3, 1969 when Hans Kocher10 and Gerald Dubois announced the Chronomatic movement, built on Buren’s micro-rotor ebauche. This would be the first Swiss automatic chronograph in customer hands, used by Breitling, Heuer, and Hamilton, which had purchased Buren in February of 1966. Hamilton-Buren was taken over by the SIHH group in 1971 and the once-great Büren factory was closed the following year, with all assets sold. This came just as the Chronomatic was gaining market traction and sadly just before the launch of Buren’s great Calbre 8211.

Universal also collaborated with Piaget, filing a joint patent in March of 1959 for a slim ratcheting winding system for micro-rotor movements. They continually updated their Microtor movement line, culminating in the 1966 introduction of the re-designed Cal. 66. Unlike the hand-made Piaget Cal. 12 P, the new Universal and Buren movements were designed for mass production and daily wear. And Universal once again beat Buren’s mark, with their ebauche measuring just 2.50 mm thick. This time Universal leaned into the thinness of the movement, matching Piaget with a new Golden Shadow watch line just 4 mm thick.

Everything changed for Universal in August of 1966, as the Bulova Watch Company of New York purchased the company. Flush with cash from the Accutron, a global phenomenon never before seen in watchmaking, Bulova sought to solidify its control over the luxury watch industry by bringing the Geneva firm under its control. Universal continued production of the Microtor family into the 1970s and even developed the world’s thinnest quartz movement in 197512. But Bulova was slow to embrace quartz as the market for the Accutron evaporated. The Universal factory in Geneva was bankrupt by the late 1970s and was sold in 1983 to new investors.

The Micro-Rotor Lives On

The micro-rotor is not dead. Far from it: There are more micro-rotor movements on the market today than ever before!

Patek Philippe filed for a patent their own micro-rotor movement in 1975, bringing their Cal. 240 to market a few years later. It has been continually updated and is one of the most-loved movements by enthusiasts like me. Chopard Manufacture leaned into the micro-rotor concept with the launch of the L.U.C movements in 1997, and it remains a highlight of the company’s offerings. A new Universal Genève launched in 2005, bringing a new Microtor (Cal. UG-100) to market in 2006. Schwarz Etienne and Parmigiani Fleurier both introduced new micro-rotor movements in 2010, and both supply these to other fine watch makers to this day. Armin Strom, Hermès, Girard-Perregaux, Bulgari, and many others have also released high-end micro-rotor movements. And Piaget never stopped developing their micro-rotor movements.

Universal was re-launched as an upscale sister brand to Breitling on April 8, 2026 and two new Microtor movements form the core of the new offerings. The new Polerouter Microtor is the first double-barrel micro-rotor movement I know of, and is a lovely tribute to Hans Kocher, who was deeply involved in both innovations. And the new Compax Microtor movement recalls the pioneering Chronomatic movement.

Research Notes

1. The question of whether Perrelet was the first to create a self-winding watch was a matter of great interest through the 20th century. Historian Alfred Chapuis uncovered many prior and subsequent designs, yet he concluded in his seminal book “La Montre Automatique Ancienne” that Perrelet absolutely deserved the credit. That being said, the self-winding watch “discovered” by Léon Leroy of Paris in 1949 may not have been created by Perrelet, according to a 1996 Europa Star article by Jean-Claude Nicolet with rebuttal by Jean-Claude Sabrier.
2. Not being a watch industry insider, Harwood may have been completely unaware that dozens of watchmakers had developed self-winding watches for over a century prior to his invention. And L. Leroy of Paris had already produced a self-winding wristwatch a year before Harwood’s patent. But he was the first to recognize the market for a wristwatch with a sealed case and self-winding movement.
3. The sliding weight concept was actually successfully revived by Pierce just after World War II. This “dissident” Moutier firm was unwilling to abide by the Swiss cartel’s production quotas, so they were blocked from working with nearly every other company. So they developed their own slim sliding-weight automatic, an amazing in-house chronograph movement, and more! In modern times we have seen another sliding-weight automatic, the Corum Golden Bridge Automatic.
4. I’m not a Rolex expert, but I am confounded by the lack of definitive history for this most-important watchmaker. The earliest mention I could find of the Oyster Perpetual comes from Journal Suisse d’Horlogerie in September of 1934, and it was fully illustrated in January of 1936. Given that Rolex trademarked the name in 1932, I guess that places the introduction of the Rolex Perpetual movement in 1933 or 1934. It definitely wasn’t 1931, despite countless blog posts and Rolex’s own advertising.
5. Incredibly, some of the earliest known self-winding pocket watch movements also have clever bi-directional winding solutions: The four controversial maybe-Perrelet movements have a pawl winding system similar to the much-later Pellaton and Magic Lever, and many of the “shaker” movements had bi-directional winding too. But Felsa’s elegant Bidynator inspired the whole industry to adopt this concept. Surprisingly, modern movements are dropping bi-directional winding, finding that it’s not actually all that useful.
6. Ball bearing support for a winding rotor was patented in 1929. But these typically placed the bearings at the periphery, supporting the rotor itself. ETA’s original Eternamatic was a tiny movement for ladies watches so the engineers brought the ball bearings to the center. Seeing how well it worked, the “five balls” became the logo of Eterna!
7. I should clarify that the name of the town is “Büren an der Aare” and it is commonly called “Büren”. But the brand name of the watch company, officially adopted by H. Williamson in 1916, was “Buren Watch Company” without the umlaut. This was generally used by the company through the 1960s, though they sometimes did include the umlaut in advertising and public communication. Confusingly, most patents list it using the Anglicized form of the name of the town, “Bueren Watch Company.” I try to be consistent (or perhaps confusing) and use “Büren” to refer to the town and “Buren” to refer to the company.
8. Oops! The Fabrique d’Horlogerie de Fontainemelon was working on another thin automatic winding system at the same time, filing patents on their peripheral rotor on September 11, 1956. This was before the announcement or publication of the micro-rotor, and they no-doubt thought that their “Fontomatic” Cal. 65 would be the thinnest automatic movement at just 4.5 mm. This came to market in 1959 as the Sandoz 333, and advertisements for this latecomer specifically neglect to mention that number, which was surpassed a year earlier by both Buren and Universal.
9. Buren trademarked “Intra Matic” in 1964 and used this name in the 1965 launch. But they also used “Intramatic” in this period, variously using both names. They had a sub-model called the “Intramatic Polestar” or “Intra Matic Pole-Star” in the 1960s as well, and I can’t imagine Universal loved this name.
10. This would be Hans Kocher-Aeschbacher, the son, rather than his father Hans Kocher-Rinner, who retired that same year. The younger Hans Kocher was a truly remarkable man, deserving of a Prix Gaïa award in all three categories: Watchmaker, businessman, and historian. He was also incredibly magnanimous, not giving undue attention in his industry history writing and speaking to the Buren “planetary rotor” despite considering it his life’s greatest work.
11. I’m wearing my Buren Calibre 82 watch as I write this!
12. The 1975 Golden Shadow and White Shadow Quartz movement measured 3.45 mm thick. It was rapidly surpassed by Citizen, just under 1 mm in 1978, Seiko, 0.90 mm that same year, and the incredible Swiss Delirium movements.

The Backward Evolution of the Rotating Bezel

Not everything gets more complicated as it evolves. The bezel, once a simple frame around the glass of a watch, became an integrated mechanism before it evolved into a simple numeric scale. From alarm clocks, navigational computers, and slide rules it became the most-recognized feature of the most iconic watches. Let’s consider the history of the rotating bezel.

From Complex to Simple

We tend to think that innovation starts with simple ideas and becomes more complex over time. Surprisingly, the opposite is usually true. Lacking a clear use case, inventors tend to start with a complex concept before stripping away less-useful elements. Consider the Apple Newton, a full-featured handheld computer with dozens of innovative ideas that inspired simpler PDAs before morphing into the modern smartphone. My 2017 BMW i3 electric is truly an exotic car, built like a carbon fiber science project and entirely unlike the conventional 2027 i3 sedan.

The same is true in watchmaking, and this brings us to the humble rotating bezel. Nearly every brand has a dive watch styled after the Rolex Submariner with a bold black knurled rotating bezel marked with triangles, sticks, and numerals. Most buyers never give these a second look, let alone turn them to time a drive, let alone a dive. Some brands also make a watch styled after the Breitling Navitimer with a busy two-part bezel marked with confusing aeronautical indications of speed and fuel load. Rolex even created a functional rotating bezel for the 2012 Sky-Dweller, used to select different functions.

A bit of research reveals that the history of the humble rotating bezel runs exactly counter to expectation, beginning with functional complications before proceeding to obscure slide rules before being stripped down to a basic hour indicator. It took 50 years for the rotating bezel to be simplified enough to enter the public consciousness and that long again before Rolex invented the Sky-Dweller’s ring command. Like so many innovations, there’s a lot to learn if you look into the rotating bezel!

The Functional Bezel

The bezel itself was an innovation. Most early clocks and watches were “open faced”, but by the 17th century some included a glass to protect the dial and hands. This was mounted in a frame of metal called a bezel, which was often attached to the case with a hinge. Thus, the first bezel was a functional part of the case, if not the watch movement.

Watches in the 19th century adopted setting and winding using a crown and often had a fixed glass over the dial, since the hands no longer needed to be manually manipulated. The glass was set directly into the rounded case without a separate bezel. This gave the watch a smooth curving contour that felt in the hand like a bar of soap (“savonnette” in French). Some watches still featured a bezel around the glass, notably the screw-on bezel and back produced by Keystone and others in America.

Winding and setting functions were not unified in a single crown until the 20th century. Earlier watches often had keys for winding or were set manually by rotating the hands. Pendant winding using a crown became widespread in the 19th century, and inventors were constantly working to enable hand setting by rotating the crown as well. These often involved levers or buttons, but some involved a rotating knurled bezel very similar in concept to the modern Sky-Dweller.

As alarm watches became popular in the early 20th century, a question arose about how to set this additional function. Attention again turned to the bezel, which could be rotated to set the time of the alarm. This must have been fairly common, as 1907 coverage of a new alarm watch from F. Schweizer & Cie discusses the limitations of bezel-set alarms (reliability and accuracy).

This was notably used by Eterna on their innovative if unsuccessful 1914 Cal. 68, the first alarm wristwatch. This 13 ligne movement was offered in a small pocket watch, a wristwatch, and a convertible watch that could be mounted on the steering wheel of a car. Although the wristwatch didn’t sell well, Eterna used the same movement in a line of successful travel alarm clocks, and these inspired the entire industry to adopt this mechanism.

Soon, most alarm clocks used a rotating bezel to set the time, often with an indicator on the bezel to show the current setting. This complicated mechanism was the first widely-used rotating bezel, pre-dating the dive watch craze by three decades.

A similar system was employed by John Harwood to set the time his Perpetual, the first self-winding wristwatch. The primary driver for his invention was the need to prevent dust and moisture from damaging the movement, a common issue on the battlefields of World War I. Since sealed crowns and stems had not yet been developed, Harwood’s goal was to create a sealed case with no crown, and he was inspired by the alarm clock setting mechanism created by Eterna to use a rotating bezel to set the time.

The Harwood Perpetual was a global sensation, even if it ultimately did not find many buyers. And the knurled or fluted bezel became a common look in the 1930s, adopted by other waterproof watch cases like the Rolex Oyster. Although not a rotating bezel in the strictest sense, many of these could be unscrewed to access the hands, dial, and movement during assembly and servicing.

It is easy to see how the Harwood Perpetual inspired the legendary Rolex Oyster Perpetual, and Rolex agreed: They specifically cited Harwood along with Abraham-Louis Perrelet as inspiration for their Oyster Perpetual in a series of advertisements in the 1950s. And it wasn’t just the Perpetual name or centrally-rotating winding: Rolex popularized the rotating bezel in this same time period, introducing the Turn-o-Graph, Submariner, and GMT-Master, as we will discuss in a moment. All of these feature a bezel that strongly resembles the Harwood Perpetual.

Lindbergh, Longines, and Weems

The idea that a rotating bezel could serve as an indicator of information rather than a mechanism to set the time originates with American aviator Philip Van Horn Weems. He developed a simplified navigational system for aircraft while serving in the American Navy in the 1920s and early 1930s. His system relied on a so-called “second-setting watch” featured a rotating inner dial that could be set to a time signal over the radio. This was based on Longines’ 1918 Touran pocket watch, which was designed to be re-set to zero at sunset to approximate the Alla Turca timekeeping system of the Ottoman Empire.

A close collaboration between Weems, aviation pioneer Charles Lindburgh, Longines-Wittnauer director John P.V. Heinmuller, and the Longines and Fluckiger factories in Saint-Imier resulted in a revolutionary watch that allowed pilots to determine their location using markings on a rotating bezel. This began with a specially-modified version of the Touran watch with an outer chapter scale showing units of arc, delivered in 1930. In 1931 Longines added a rotating bezel marked with units of arc in red and green. This bezel would be pre-positioned according to the equation of time table to instantly perform the calculation needed to determine the Greenwich Hour Angle of the Sun.

Once Longines developed a stop-seconds flyback movement the inner rotating dial component was no longer needed, allowing all calculations to be performed using the rotating bezel. Later versions even dispensed with the units of arc markings on the bezel, using a simple scale with units marked 10 through 60. These were no longer Hour Angle watches at all, but they were some of the first watches with a rotating bezel. In later decades Longines produced faithful reproductions of the Lindbergh Hour Angle watch, including a lovely limited edition in 2018.

The Evolving Chronograph Bezel

As the world industrialized in the early 20th century, a need for time measurement appeared. Businesses were more interested in tracking efficiency, and aviators needed to record and note time of travel. Watchmakers struggled to develop affordable and reliable chronograph mechanisms in the 1930s and 1940s, and this a fascinating area of study. This was the era when the old monopusher gave way to the Compax, flyback, and chronostop.

The alarm time indicators of previous decades gave innovators a new idea: A rotating bezel could set an indicator to measure elapsed time. In 1935 Heuer introduced a new chronograph for aviators that featured a knurled rotating bezel attached to a white triangular indicator “to mark the departure time or any other observation.” It is unclear if this is the first chronograph watch with a rotating bezel, but it is the earliest our research has uncovered.

Breitling produced a similar-looking aviation watch with a rotating bezel in early 1936. Unlike the Heuer chronograph, the Breitling model has no minute totalizer, only chronograph seconds. As noted in Journal Suisse d’Horlogerie, the bezel indicator would “serve as the minute totalizer”, synchronized with the running minutes hand for timing flight operations.

Fortis also produced a chronostop watch with a rotating bezel in 1936. This movement had a stop and reset function for the central chronograph seconds hand using a pusher in the crown. The Fortis chronostop was the first watch we’ve seen with a full set of 60 markers on the rotating bezel, complete with numerals from 5 to 60. The design also departed from the classic rounded screw-on bezel look: It has a flat bezel that aligns with the dial along with a sharp vertical knurled edge.

The 1938 Damas Ref. 2452 dispensed with the expensive chronograph movement entirely, relying solely on a rotating bezel and central running seconds hand to record elapsed time. This watch advanced the bezel markings in a significant way: It features a triangle at the top rather than 0 or 60. This is a common design today, combining the Heuer and Breitling bezel indicator with the full minute track and vertical edge seen on the Fortis chronostop.

The next major advancement in bezel design came from Invicta, then a respected maker of complicated watches in La Chaux-de-Fonds. They introduced two models for 1940 with a deeply-grooved 12-hour bezel: The Secontrol had a chronostop movement and telemeter and tachymeter scales on the dial, while the Time-Log used a start-stop chronograph movement with three pushers. The new bezel served as an hour counter for these watches, which would be much more useful in association with the minute totalizer subdial on the Time-Log. It is unclear exactly how the 12-hour bezel would be useful on the Secontrol.

The next important advance in simple bezel design came in 1949 with the Minerva Ref. 1527, which features numerals that count down rather than up. This is useful as a reminder for future events rather than a recorder of elapsed time. Since this model is marked from 1 to 11 (again with the triangle at 12), it was designed to be used by aviators to mark the next turn using the hour hand. Count-down bezels are uncommon today but they remain an interesting variation on the theme.

The Slide Rule Bezel

The slide rule (“règle à calcul” in French) was invented by English mathematician and clergyman Reverend William Oughtred and others in the 17th century, utilizing the mathematical concept of logarithms discovered by John Napier. Logarithms exploit the relationship between two scales to perform various calculations, especially multiplication and division. Slide rules were the most convenient and accurate mathematical tool until the creation of electronic calculators and computers in the 1960s.

The straight slide rule is most familiar but the circular slide rule has existed since the 19th century. In 1905, Emile Alexandre Moret of France received a patent for a mechanical calculator that used geared hands to perform logarithmic calculations using circular disks. Moret recognized that a circular slide rule could be packaged as a clock or watch, calling his invention a “montre à calcul”, but it did not include a timekeeping function.

Zénith, the famous Le Locle watchmaking firm, received a patent for a mechanical slide rule calculator in a pocket watch case in 1918. Once again, although this resembled a watch it was actually a pocket calculator without any timekeeping capability.

Importantly, both of these designs appeared before the Harwood Perpetual watch popularized the concept of a rotating bezel. It was only a matter of time before someone moved the circular slide rule to the bezel of a watch.

Graef & Cie, Fabrique Mimo, was one of the most innovative watchmaking companies in the first half of the 20th century, introducing many firsts between 1930 and 1941: The first wristwatch with a calendar, a double-barrel 8-day movement, a digital jump-hour display, and even a quick-change strap. So it is no surprise that Mimo was also the first company to produce a wristwatch with a slide rule bezel.

The Mimo-Loga was the first watch to feature a freely-rotating bezel, and it included classic slide rule markings. The July 27, 1940 patent eloquently describes that, “in addition to the chronometric and chronograph devices, includes at least two conjugate logarithmic scales, at least one of which is mounted on a rotating member concentric with the dial that carries the other.”

The Mimo-Loga was introduced in early 1941, just before Mimo founder Otto Graef retired. He left his sons in control of Mimo to his sons, but they were more interested in re-establishing the famous Girard-Perregaux brand, which the family acquired in 1928. Despite its history of innovation, the Mimo brand soon disappeared.

One watch comes to mind when we think of the slide rule bezel today: The Breitling Navitimer. Although Breitling is correctly credited with making the slide rule bezel famous, it was introduced with the Chronomat, not the Navitimer, and just a few months after the Mimo-Loga! Let’s set the record straight.

Most contemporary accounts claim that Breitling introduced the Chronomat in 1942, but primary sources include advertisements for “Le Chronomat” in September 1941. Although the watch may not have entered production this early, it was clearly a focus for the company at this time. Like the Mimo-Loga, the Chronomat had slide rule markings on the rotating bezel. But Breitling’s watch used a chronograph movement, and this allowed the wearer to perform many more useful calculations.

Breitling produced a companion booklet to help buyers make the most of the Chronomat’s capabilities. The dial also included red reference markings to assist in measuring seconds, fifths, minutes, and hours as well as a telemeter indicator. The Chronomat was specifically designed as a tachymeter, telemeter, pulsometer, and metronome, and the scale could perform standard mathematical calculations like previous circular slide rules. Breitling even produced a cardboard cutout model, available to retailers to help demonstrate these functions.

The Chronomat name combined these capabilities, “chronograph” and “mathematics”, but this did not last long. An automatic Chronomat without a chronograph function was introduced by 1954 and the famous Chronomatic movement further muddied the waters. Today the Chronomat line includes many chronographs but not one has a slide rule bezel.

This brings us to the most famous slide rule watch, the Breitling Navitimer. Today, the company claims that this watch was created in 1952 and released in 1954 with AOPA branding, and we have no reason to doubt their internal records. But the earliest public references to the Navitimer appear in 1955, and the trademark for the name was received on January 22 of that year. The Navitimer is a specialized watch, originally exclusively available to pilots, and may not have been publicized or even named until 1955.

While the Chronomat had indicators for various capabilities, the Navitimer was designed specifically to perform specialized calculations related to air travel: Ground speed, distance per minute, fuel consumption, rate and distance of climb or descent, and nautical and statute mile conversion. These scales and indices made for a very busy dial despite the hefty 41 mm case. Breitling’s current lineup includes a variety of beautiful and colorful interpretations of the classic Navitimer.

Incredibly, it is this specialized tool watch design that has become dominant in the public consciousness. Today there are numerous “Navitimer” style watches made by brands like Casio, Citizen, Hamilton, Seiko, and Victorinox. The Sinn 903 also deserves special mention: They bought up the remaining Navitimer stock from Breitling in 1979 and continued to sell these original watches as their Navigation Timer into the 1980s. This has remained in production today, with the Model 903 II released in March of 2024.

Rolex: Turn-o-Graph, Submariner, and GMT-Master

When the Swiss Industries Fair in Basel opened on May 8, 1954, visitors to the Rolex stand were treated to three new product releases: Explorer, Submariner, and Turn-o-Graph. These watches marked a transition for Rolex and ultimately the entire watch industry. All three were tool watches with modern Oyster cases and Perpetual movements, and two were defined by their distinctive rotating bezels.

The Turn-o-Graph name is not well-remembered today, but it was a staple of the Rolex lineup (on and off) until 2011. It was a simple time-only watch with a rotating bezel designed to calculate elapsed time. The Rolex rotating bezel was mostly flat, with a sharp knurled edge. In the Turn-o-Graph it was marked with four dots then a stick or numerals at 10, 20, 30, 40, and 50. A triangle with a luminous dot was placed at the top. This design reflected the dial, which used dots on the hour, sticks at 3, 6, and 9, and a triangle at 12, all with luminous paint. The Turn-o-Graph was thus the most harmonious of the trio.

The Submariner was very similar to the Turn-o-Graph but was rated to 200 meters. Rolex had a long history of producing waterproof watches, but the Submariner was altogether more elegant and refined. The bezel was wide and flat, lacking the dots of the Turn-o-Graph, with stick markers alternating between numerals on the 10s. Although a true icon today, this original Submariner looked like nothing else on the market at the time. The look was soon copied by the entire industry, making the simple flat rotating bezel a sports watch staple. And the Submariner is undoubtedly one of the most in-demand watches globally to this day.

On March 22, 1956, Rolex founder Hans Wilsdorf gathered friends and industry figures to the Hôtel des Bergues in Geneva to celebrate his 75th birthday and the success of the company. Along with the “Stick-o-Matic”, presented to him by the factory, the crowd was able to see a brand new Rolex model.

The GMT-Master was developed with the needs of pilots in mind, though Rolex did not go to the same extremes as the Breitling Navitimer. It was the first Rolex to feature a 24 hour hand, though it was not adjustable until the 1983 GMT-Master II. And it also included a date window under a magnifying glass bubble at 3 on the dial. But it is the rotating bezel that we will focus on, since that is the subject of this article.

Mechanically quite similar to the Submariner bezel, the GMT-Master featured alternating dots and numerals from 2 to 22, indicating the hours for the central 24 hour hand. In this way, it could be used to show the time in a second time zone by rotating the bezel ahead or behind the fixed hand. This too would become an iconic design, copied by many other firms in the coming decades. And it remains a favorite Rolex model today.

From Complex to Simple, With Many Variations

There is far more we could say about the rotating bezel, but perhaps this is enough to prove my point: Invention often proceeds from complex to simple. What was once an integrated mechanism to set the alarm or time became a simple alternate time scale. But there is subtlety to the rotating bezel! While most count up, some count down. While most are marked at 60 minute intervals, others are marked at 12. And some function as slide rules or perform complicated calculations specific to navigation. The simple bezel is far from simple, and many different companies and inventors were involved in its evolution!

The Backward Evolution of the Rotating Bezel

Not everything gets more complicated as it evolves. The bezel, once a simple frame around the glass of a watch, became an integrated mechanism before it evolved into a simple numeric scale. From alarm clocks, navigational computers, and slide rules it became the most-recognized feature of the most iconic watches. Let’s consider the history of the rotating bezel.

From Complex to Simple

We tend to think that innovation starts with simple ideas and becomes more complex over time. Surprisingly, the opposite is usually true. Lacking a clear use case, inventors tend to start with a complex concept before stripping away less-useful elements. Consider the Apple Newton, a full-featured handheld computer with dozens of innovative ideas that inspired simpler PDAs before morphing into the modern smartphone. My 2017 BMW i3 electric is truly an exotic car, built like a carbon fiber science project and entirely unlike the conventional 2027 i3 sedan.

The same is true in watchmaking, and this brings us to the humble rotating bezel. Nearly every brand has a dive watch styled after the Rolex Submariner with a bold black knurled rotating bezel marked with triangles, sticks, and numerals. Most buyers never give these a second look, let alone turn them to time a drive, let alone a dive. Some brands also make a watch styled after the Breitling Navitimer with a busy two-part bezel marked with confusing aeronautical indications of speed and fuel load. Rolex even created a functional rotating bezel for the 2012 Sky-Dweller, used to select different functions.

A bit of research reveals that the history of the humble rotating bezel runs exactly counter to expectation, beginning with functional complications before proceeding to obscure slide rules before being stripped down to a basic hour indicator. It took 50 years for the rotating bezel to be simplified enough to enter the public consciousness and that long again before Rolex invented the Sky-Dweller’s ring command. Like so many innovations, there’s a lot to learn if you look into the rotating bezel!

The Functional Bezel

The bezel itself was an innovation. Most early clocks and watches were “open faced”, but by the 17th century some included a glass to protect the dial and hands. This was mounted in a frame of metal called a bezel, which was often attached to the case with a hinge. Thus, the first bezel was a functional part of the case, if not the watch movement.

Watches in the 19th century adopted setting and winding using a crown and often had a fixed glass over the dial, since the hands no longer needed to be manually manipulated. The glass was set directly into the rounded case without a separate bezel. This gave the watch a smooth curving contour that felt in the hand like a bar of soap (“savonnette” in French). Some watches still featured a bezel around the glass, notably the screw-on bezel and back produced by Keystone and others in America.

Winding and setting functions were not unified in a single crown until the 20th century. Earlier watches often had keys for winding or were set manually by rotating the hands. Pendant winding using a crown became widespread in the 19th century, and inventors were constantly working to enable hand setting by rotating the crown as well. These often involved levers or buttons, but some involved a rotating knurled bezel very similar in concept to the modern Sky-Dweller.

As alarm watches became popular in the early 20th century, a question arose about how to set this additional function. Attention again turned to the bezel, which could be rotated to set the time of the alarm. This must have been fairly common, as 1907 coverage of a new alarm watch from F. Schweizer & Cie discusses the limitations of bezel-set alarms (reliability and accuracy).

This was notably used by Eterna on their innovative if unsuccessful 1914 Cal. 68, the first alarm wristwatch. This 13 ligne movement was offered in a small pocket watch, a wristwatch, and a convertible watch that could be mounted on the steering wheel of a car. Although the wristwatch didn’t sell well, Eterna used the same movement in a line of successful travel alarm clocks, and these inspired the entire industry to adopt this mechanism.

Soon, most alarm clocks used a rotating bezel to set the time, often with an indicator on the bezel to show the current setting. This complicated mechanism was the first widely-used rotating bezel, pre-dating the dive watch craze by three decades.

A similar system was employed by John Harwood to set the time his Perpetual, the first self-winding wristwatch. The primary driver for his invention was the need to prevent dust and moisture from damaging the movement, a common issue on the battlefields of World War I. Since sealed crowns and stems had not yet been developed, Harwood’s goal was to create a sealed case with no crown, and he was inspired by the alarm clock setting mechanism created by Eterna to use a rotating bezel to set the time.

The Harwood Perpetual was a global sensation, even if it ultimately did not find many buyers. And the knurled or fluted bezel became a common look in the 1930s, adopted by other waterproof watch cases like the Rolex Oyster. Although not a rotating bezel in the strictest sense, many of these could be unscrewed to access the hands, dial, and movement during assembly and servicing.

It is easy to see how the Harwood Perpetual inspired the legendary Rolex Oyster Perpetual, and Rolex agreed: They specifically cited Harwood along with Abraham-Louis Perrelet as inspiration for their Oyster Perpetual in a series of advertisements in the 1950s. And it wasn’t just the Perpetual name or centrally-rotating winding: Rolex popularized the rotating bezel in this same time period, introducing the Turn-o-Graph, Submariner, and GMT-Master, as we will discuss in a moment. All of these feature a bezel that strongly resembles the Harwood Perpetual.

Lindbergh, Longines, and Weems

The idea that a rotating bezel could serve as an indicator of information rather than a mechanism to set the time originates with American aviator Philip Van Horn Weems. He developed a simplified navigational system for aircraft while serving in the American Navy in the 1920s and early 1930s. His system relied on a so-called “second-setting watch” featured a rotating inner dial that could be set to a time signal over the radio. This was based on Longines’ 1918 Touran pocket watch, which was designed to be re-set to zero at sunset to approximate the Alla Turca timekeeping system of the Ottoman Empire.

A close collaboration between Weems, aviation pioneer Charles Lindburgh, Longines-Wittnauer director John P.V. Heinmuller, and the Longines and Fluckiger factories in Saint-Imier resulted in a revolutionary watch that allowed pilots to determine their location using markings on a rotating bezel. This began with a specially-modified version of the Touran watch with an outer chapter scale showing units of arc, delivered in 1930. In 1931 Longines added a rotating bezel marked with units of arc in red and green. This bezel would be pre-positioned according to the equation of time table to instantly perform the calculation needed to determine the Greenwich Hour Angle of the Sun.

Once Longines developed a stop-seconds flyback movement the inner rotating dial component was no longer needed, allowing all calculations to be performed using the rotating bezel. Later versions even dispensed with the units of arc markings on the bezel, using a simple scale with units marked 10 through 60. These were no longer Hour Angle watches at all, but they were some of the first watches with a rotating bezel. In later decades Longines produced faithful reproductions of the Lindbergh Hour Angle watch, including a lovely limited edition in 2018.

The Evolving Chronograph Bezel

As the world industrialized in the early 20th century, a need for time measurement appeared. Businesses were more interested in tracking efficiency, and aviators needed to record and note time of travel. Watchmakers struggled to develop affordable and reliable chronograph mechanisms in the 1930s and 1940s, and this a fascinating area of study. This was the era when the old monopusher gave way to the Compax, flyback, and chronostop.

The alarm time indicators of previous decades gave innovators a new idea: A rotating bezel could set an indicator to measure elapsed time. In 1935 Heuer introduced a new chronograph for aviators that featured a knurled rotating bezel attached to a white triangular indicator “to mark the departure time or any other observation.” It is unclear if this is the first chronograph watch with a rotating bezel, but it is the earliest our research has uncovered.

Breitling produced a similar-looking aviation watch with a rotating bezel in early 1936. Unlike the Heuer chronograph, the Breitling model has no minute totalizer, only chronograph seconds. As noted in Journal Suisse d’Horlogerie, the bezel indicator would “serve as the minute totalizer”, synchronized with the running minutes hand for timing flight operations.

Fortis also produced a chronostop watch with a rotating bezel in 1936. This movement had a stop and reset function for the central chronograph seconds hand using a pusher in the crown. The Fortis chronostop was the first watch we’ve seen with a full set of 60 markers on the rotating bezel, complete with numerals from 5 to 60. The design also departed from the classic rounded screw-on bezel look: It has a flat bezel that aligns with the dial along with a sharp vertical knurled edge.

The 1938 Damas Ref. 2452 dispensed with the expensive chronograph movement entirely, relying solely on a rotating bezel and central running seconds hand to record elapsed time. This watch advanced the bezel markings in a significant way: It features a triangle at the top rather than 0 or 60. This is a common design today, combining the Heuer and Breitling bezel indicator with the full minute track and vertical edge seen on the Fortis chronostop.

The next major advancement in bezel design came from Invicta, then a respected maker of complicated watches in La Chaux-de-Fonds. They introduced two models for 1940 with a deeply-grooved 12-hour bezel: The Secontrol had a chronostop movement and telemeter and tachymeter scales on the dial, while the Time-Log used a start-stop chronograph movement with three pushers. The new bezel served as an hour counter for these watches, which would be much more useful in association with the minute totalizer subdial on the Time-Log. It is unclear exactly how the 12-hour bezel would be useful on the Secontrol.

The next important advance in simple bezel design came in 1949 with the Minerva Ref. 1527, which features numerals that count down rather than up. This is useful as a reminder for future events rather than a recorder of elapsed time. Since this model is marked from 1 to 11 (again with the triangle at 12), it was designed to be used by aviators to mark the next turn using the hour hand. Count-down bezels are uncommon today but they remain an interesting variation on the theme.

The Slide Rule Bezel

The slide rule (“règle à calcul” in French) was invented by English mathematician and clergyman Reverend William Oughtred and others in the 17th century, utilizing the mathematical concept of logarithms discovered by John Napier. Logarithms exploit the relationship between two scales to perform various calculations, especially multiplication and division. Slide rules were the most convenient and accurate mathematical tool until the creation of electronic calculators and computers in the 1960s.

The straight slide rule is most familiar but the circular slide rule has existed since the 19th century. In 1905, Emile Alexandre Moret of France received a patent for a mechanical calculator that used geared hands to perform logarithmic calculations using circular disks. Moret recognized that a circular slide rule could be packaged as a clock or watch, calling his invention a “montre à calcul”, but it did not include a timekeeping function.

Zénith, the famous Le Locle watchmaking firm, received a patent for a mechanical slide rule calculator in a pocket watch case in 1918. Once again, although this resembled a watch it was actually a pocket calculator without any timekeeping capability.

Importantly, both of these designs appeared before the Harwood Perpetual watch popularized the concept of a rotating bezel. It was only a matter of time before someone moved the circular slide rule to the bezel of a watch.

Graef & Cie, Fabrique Mimo, was one of the most innovative watchmaking companies in the first half of the 20th century, introducing many firsts between 1930 and 1941: The first wristwatch with a calendar, a double-barrel 8-day movement, a digital jump-hour display, and even a quick-change strap. So it is no surprise that Mimo was also the first company to produce a wristwatch with a slide rule bezel.

The Mimo-Loga was the first watch to feature a freely-rotating bezel, and it included classic slide rule markings. The July 27, 1940 patent eloquently describes that, “in addition to the chronometric and chronograph devices, includes at least two conjugate logarithmic scales, at least one of which is mounted on a rotating member concentric with the dial that carries the other.”

The Mimo-Loga was introduced in early 1941, just before Mimo founder Otto Graef retired. He left his sons in control of Mimo to his sons, but they were more interested in re-establishing the famous Girard-Perregaux brand, which the family acquired in 1928. Despite its history of innovation, the Mimo brand soon disappeared.

One watch comes to mind when we think of the slide rule bezel today: The Breitling Navitimer. Although Breitling is correctly credited with making the slide rule bezel famous, it was introduced with the Chronomat, not the Navitimer, and just a few months after the Mimo-Loga! Let’s set the record straight.

Most contemporary accounts claim that Breitling introduced the Chronomat in 1942, but primary sources include advertisements for “Le Chronomat” in September 1941. Although the watch may not have entered production this early, it was clearly a focus for the company at this time. Like the Mimo-Loga, the Chronomat had slide rule markings on the rotating bezel. But Breitling’s watch used a chronograph movement, and this allowed the wearer to perform many more useful calculations.

Breitling produced a companion booklet to help buyers make the most of the Chronomat’s capabilities. The dial also included red reference markings to assist in measuring seconds, fifths, minutes, and hours as well as a telemeter indicator. The Chronomat was specifically designed as a tachymeter, telemeter, pulsometer, and metronome, and the scale could perform standard mathematical calculations like previous circular slide rules. Breitling even produced a cardboard cutout model, available to retailers to help demonstrate these functions.

The Chronomat name combined these capabilities, “chronograph” and “mathematics”, but this did not last long. An automatic Chronomat without a chronograph function was introduced by 1954 and the famous Chronomatic movement further muddied the waters. Today the Chronomat line includes many chronographs but not one has a slide rule bezel.

This brings us to the most famous slide rule watch, the Breitling Navitimer. Today, the company claims that this watch was created in 1952 and released in 1954 with AOPA branding, and we have no reason to doubt their internal records. But the earliest public references to the Navitimer appear in 1955, and the trademark for the name was received on January 22 of that year. The Navitimer is a specialized watch, originally exclusively available to pilots, and may not have been publicized or even named until 1955.

While the Chronomat had indicators for various capabilities, the Navitimer was designed specifically to perform specialized calculations related to air travel: Ground speed, distance per minute, fuel consumption, rate and distance of climb or descent, and nautical and statute mile conversion. These scales and indices made for a very busy dial despite the hefty 41 mm case. Breitling’s current lineup includes a variety of beautiful and colorful interpretations of the classic Navitimer.

Incredibly, it is this specialized tool watch design that has become dominant in the public consciousness. Today there are numerous “Navitimer” style watches made by brands like Casio, Citizen, Hamilton, Seiko, and Victorinox. The Sinn 903 also deserves special mention: They bought up the remaining Navitimer stock from Breitling in 1979 and continued to sell these original watches as their Navigation Timer into the 1980s. This has remained in production today, with the Model 903 II released in March of 2024.

Rolex: Turn-o-Graph, Submariner, and GMT-Master

When the Swiss Industries Fair in Basel opened on May 8, 1954, visitors to the Rolex stand were treated to three new product releases: Explorer, Submariner, and Turn-o-Graph. These watches marked a transition for Rolex and ultimately the entire watch industry. All three were tool watches with modern Oyster cases and Perpetual movements, and two were defined by their distinctive rotating bezels.

The Turn-o-Graph name is not well-remembered today, but it was a staple of the Rolex lineup (on and off) until 2011. It was a simple time-only watch with a rotating bezel designed to calculate elapsed time. The Rolex rotating bezel was mostly flat, with a sharp knurled edge. In the Turn-o-Graph it was marked with four dots then a stick or numerals at 10, 20, 30, 40, and 50. A triangle with a luminous dot was placed at the top. This design reflected the dial, which used dots on the hour, sticks at 3, 6, and 9, and a triangle at 12, all with luminous paint. The Turn-o-Graph was thus the most harmonious of the trio.

The Submariner was very similar to the Turn-o-Graph but was rated to 200 meters. Rolex had a long history of producing waterproof watches, but the Submariner was altogether more elegant and refined. The bezel was wide and flat, lacking the dots of the Turn-o-Graph, with stick markers alternating between numerals on the 10s. Although a true icon today, this original Submariner looked like nothing else on the market at the time. The look was soon copied by the entire industry, making the simple flat rotating bezel a sports watch staple. And the Submariner is undoubtedly one of the most in-demand watches globally to this day.

On March 22, 1956, Rolex founder Hans Wilsdorf gathered friends and industry figures to the Hôtel des Bergues in Geneva to celebrate his 75th birthday and the success of the company. Along with the “Stick-o-Matic”, presented to him by the factory, the crowd was able to see a brand new Rolex model.

The GMT-Master was developed with the needs of pilots in mind, though Rolex did not go to the same extremes as the Breitling Navitimer. It was the first Rolex to feature a 24 hour hand, though it was not adjustable until the 1983 GMT-Master II. And it also included a date window under a magnifying glass bubble at 3 on the dial. But it is the rotating bezel that we will focus on, since that is the subject of this article.

Mechanically quite similar to the Submariner bezel, the GMT-Master featured alternating dots and numerals from 2 to 22, indicating the hours for the central 24 hour hand. In this way, it could be used to show the time in a second time zone by rotating the bezel ahead or behind the fixed hand. This too would become an iconic design, copied by many other firms in the coming decades. And it remains a favorite Rolex model today.

From Complex to Simple, With Many Variations

There is far more we could say about the rotating bezel, but perhaps this is enough to prove my point: Invention often proceeds from complex to simple. What was once an integrated mechanism to set the alarm or time became a simple alternate time scale. But there is subtlety to the rotating bezel! While most count up, some count down. While most are marked at 60 minute intervals, others are marked at 12. And some function as slide rules or perform complicated calculations specific to navigation. The simple bezel is far from simple, and many different companies and inventors were involved in its evolution!

The Backward Evolution of the Rotating Bezel

Not everything gets more complicated as it evolves. The bezel, once a simple frame around the glass of a watch, became an integrated mechanism before it evolved into a simple numeric scale. From alarm clocks, navigational computers, and slide rules it became the most-recognized feature of the most iconic watches. Let’s consider the history of the rotating bezel.

From Complex to Simple

We tend to think that innovation starts with simple ideas and becomes more complex over time. Surprisingly, the opposite is usually true. Lacking a clear use case, inventors tend to start with a complex concept before stripping away less-useful elements. Consider the Apple Newton, a full-featured handheld computer with dozens of innovative ideas that inspired simpler PDAs before morphing into the modern smartphone. My 2017 BMW i3 electric is truly an exotic car, built like a carbon fiber science project and entirely unlike the conventional 2027 i3 sedan.

The same is true in watchmaking, and this brings us to the humble rotating bezel. Nearly every brand has a dive watch styled after the Rolex Submariner with a bold black knurled rotating bezel marked with triangles, sticks, and numerals. Most buyers never give these a second look, let alone turn them to time a drive, let alone a dive. Some brands also make a watch styled after the Breitling Navitimer with a busy two-part bezel marked with confusing aeronautical indications of speed and fuel load. Rolex even created a functional rotating bezel for the 2012 Sky-Dweller, used to select different functions.

A bit of research reveals that the history of the humble rotating bezel runs exactly counter to expectation, beginning with functional complications before proceeding to obscure slide rules before being stripped down to a basic hour indicator. It took 50 years for the rotating bezel to be simplified enough to enter the public consciousness and that long again before Rolex invented the Sky-Dweller’s ring command. Like so many innovations, there’s a lot to learn if you look into the rotating bezel!

The Functional Bezel

The bezel itself was an innovation. Most early clocks and watches were “open faced”, but by the 17th century some included a glass to protect the dial and hands. This was mounted in a frame of metal called a bezel, which was often attached to the case with a hinge. Thus, the first bezel was a functional part of the case, if not the watch movement.

Watches in the 19th century adopted setting and winding using a crown and often had a fixed glass over the dial, since the hands no longer needed to be manually manipulated. The glass was set directly into the rounded case without a separate bezel. This gave the watch a smooth curving contour that felt in the hand like a bar of soap (“savonnette” in French). Some watches still featured a bezel around the glass, notably the screw-on bezel and back produced by Keystone and others in America.

Winding and setting functions were not unified in a single crown until the 20th century. Earlier watches often had keys for winding or were set manually by rotating the hands. Pendant winding using a crown became widespread in the 19th century, and inventors were constantly working to enable hand setting by rotating the crown as well. These often involved levers or buttons, but some involved a rotating knurled bezel very similar in concept to the modern Sky-Dweller.

As alarm watches became popular in the early 20th century, a question arose about how to set this additional function. Attention again turned to the bezel, which could be rotated to set the time of the alarm. This must have been fairly common, as 1907 coverage of a new alarm watch from F. Schweizer & Cie discusses the limitations of bezel-set alarms (reliability and accuracy).

This was notably used by Eterna on their innovative if unsuccessful 1914 Cal. 68, the first alarm wristwatch. This 13 ligne movement was offered in a small pocket watch, a wristwatch, and a convertible watch that could be mounted on the steering wheel of a car. Although the wristwatch didn’t sell well, Eterna used the same movement in a line of successful travel alarm clocks, and these inspired the entire industry to adopt this mechanism.

Soon, most alarm clocks used a rotating bezel to set the time, often with an indicator on the bezel to show the current setting. This complicated mechanism was the first widely-used rotating bezel, pre-dating the dive watch craze by three decades.

A similar system was employed by John Harwood to set the time his Perpetual, the first self-winding wristwatch. The primary driver for his invention was the need to prevent dust and moisture from damaging the movement, a common issue on the battlefields of World War I. Since sealed crowns and stems had not yet been developed, Harwood’s goal was to create a sealed case with no crown, and he was inspired by the alarm clock setting mechanism created by Eterna to use a rotating bezel to set the time.

The Harwood Perpetual was a global sensation, even if it ultimately did not find many buyers. And the knurled or fluted bezel became a common look in the 1930s, adopted by other waterproof watch cases like the Rolex Oyster. Although not a rotating bezel in the strictest sense, many of these could be unscrewed to access the hands, dial, and movement during assembly and servicing.

It is easy to see how the Harwood Perpetual inspired the legendary Rolex Oyster Perpetual, and Rolex agreed: They specifically cited Harwood along with Abraham-Louis Perrelet as inspiration for their Oyster Perpetual in a series of advertisements in the 1950s. And it wasn’t just the Perpetual name or centrally-rotating winding: Rolex popularized the rotating bezel in this same time period, introducing the Turn-o-Graph, Submariner, and GMT-Master, as we will discuss in a moment. All of these feature a bezel that strongly resembles the Harwood Perpetual.

Lindbergh, Longines, and Weems

The idea that a rotating bezel could serve as an indicator of information rather than a mechanism to set the time originates with American aviator Philip Van Horn Weems. He developed a simplified navigational system for aircraft while serving in the American Navy in the 1920s and early 1930s. His system relied on a so-called “second-setting watch” featured a rotating inner dial that could be set to a time signal over the radio. This was based on Longines’ 1918 Touran pocket watch, which was designed to be re-set to zero at sunset to approximate the Alla Turca timekeeping system of the Ottoman Empire.

A close collaboration between Weems, aviation pioneer Charles Lindburgh, Longines-Wittnauer director John P.V. Heinmuller, and the Longines and Fluckiger factories in Saint-Imier resulted in a revolutionary watch that allowed pilots to determine their location using markings on a rotating bezel. This began with a specially-modified version of the Touran watch with an outer chapter scale showing units of arc, delivered in 1930. In 1931 Longines added a rotating bezel marked with units of arc in red and green. This bezel would be pre-positioned according to the equation of time table to instantly perform the calculation needed to determine the Greenwich Hour Angle of the Sun.

Once Longines developed a stop-seconds flyback movement the inner rotating dial component was no longer needed, allowing all calculations to be performed using the rotating bezel. Later versions even dispensed with the units of arc markings on the bezel, using a simple scale with units marked 10 through 60. These were no longer Hour Angle watches at all, but they were some of the first watches with a rotating bezel. In later decades Longines produced faithful reproductions of the Lindbergh Hour Angle watch, including a lovely limited edition in 2018.

The Evolving Chronograph Bezel

As the world industrialized in the early 20th century, a need for time measurement appeared. Businesses were more interested in tracking efficiency, and aviators needed to record and note time of travel. Watchmakers struggled to develop affordable and reliable chronograph mechanisms in the 1930s and 1940s, and this a fascinating area of study. This was the era when the old monopusher gave way to the Compax, flyback, and chronostop.

The alarm time indicators of previous decades gave innovators a new idea: A rotating bezel could set an indicator to measure elapsed time. In 1935 Heuer introduced a new chronograph for aviators that featured a knurled rotating bezel attached to a white triangular indicator “to mark the departure time or any other observation.” It is unclear if this is the first chronograph watch with a rotating bezel, but it is the earliest our research has uncovered.

Breitling produced a similar-looking aviation watch with a rotating bezel in early 1936. Unlike the Heuer chronograph, the Breitling model has no minute totalizer, only chronograph seconds. As noted in Journal Suisse d’Horlogerie, the bezel indicator would “serve as the minute totalizer”, synchronized with the running minutes hand for timing flight operations.

Fortis also produced a chronostop watch with a rotating bezel in 1936. This movement had a stop and reset function for the central chronograph seconds hand using a pusher in the crown. The Fortis chronostop was the first watch we’ve seen with a full set of 60 markers on the rotating bezel, complete with numerals from 5 to 60. The design also departed from the classic rounded screw-on bezel look: It has a flat bezel that aligns with the dial along with a sharp vertical knurled edge.

The 1938 Damas Ref. 2452 dispensed with the expensive chronograph movement entirely, relying solely on a rotating bezel and central running seconds hand to record elapsed time. This watch advanced the bezel markings in a significant way: It features a triangle at the top rather than 0 or 60. This is a common design today, combining the Heuer and Breitling bezel indicator with the full minute track and vertical edge seen on the Fortis chronostop.

The next major advancement in bezel design came from Invicta, then a respected maker of complicated watches in La Chaux-de-Fonds. They introduced two models for 1940 with a deeply-grooved 12-hour bezel: The Secontrol had a chronostop movement and telemeter and tachymeter scales on the dial, while the Time-Log used a start-stop chronograph movement with three pushers. The new bezel served as an hour counter for these watches, which would be much more useful in association with the minute totalizer subdial on the Time-Log. It is unclear exactly how the 12-hour bezel would be useful on the Secontrol.

The next important advance in simple bezel design came in 1949 with the Minerva Ref. 1527, which features numerals that count down rather than up. This is useful as a reminder for future events rather than a recorder of elapsed time. Since this model is marked from 1 to 11 (again with the triangle at 12), it was designed to be used by aviators to mark the next turn using the hour hand. Count-down bezels are uncommon today but they remain an interesting variation on the theme.

The Slide Rule Bezel

The slide rule (“règle à calcul” in French) was invented by English mathematician and clergyman Reverend William Oughtred and others in the 17th century, utilizing the mathematical concept of logarithms discovered by John Napier. Logarithms exploit the relationship between two scales to perform various calculations, especially multiplication and division. Slide rules were the most convenient and accurate mathematical tool until the creation of electronic calculators and computers in the 1960s.

The straight slide rule is most familiar but the circular slide rule has existed since the 19th century. In 1905, Emile Alexandre Moret of France received a patent for a mechanical calculator that used geared hands to perform logarithmic calculations using circular disks. Moret recognized that a circular slide rule could be packaged as a clock or watch, calling his invention a “montre à calcul”, but it did not include a timekeeping function.

Zénith, the famous Le Locle watchmaking firm, received a patent for a mechanical slide rule calculator in a pocket watch case in 1918. Once again, although this resembled a watch it was actually a pocket calculator without any timekeeping capability.

Importantly, both of these designs appeared before the Harwood Perpetual watch popularized the concept of a rotating bezel. It was only a matter of time before someone moved the circular slide rule to the bezel of a watch.

Graef & Cie, Fabrique Mimo, was one of the most innovative watchmaking companies in the first half of the 20th century, introducing many firsts between 1930 and 1941: The first wristwatch with a calendar, a double-barrel 8-day movement, a digital jump-hour display, and even a quick-change strap. So it is no surprise that Mimo was also the first company to produce a wristwatch with a slide rule bezel.

The Mimo-Loga was the first watch to feature a freely-rotating bezel, and it included classic slide rule markings. The July 27, 1940 patent eloquently describes that, “in addition to the chronometric and chronograph devices, includes at least two conjugate logarithmic scales, at least one of which is mounted on a rotating member concentric with the dial that carries the other.”

The Mimo-Loga was introduced in early 1941, just before Mimo founder Otto Graef retired. He left his sons in control of Mimo to his sons, but they were more interested in re-establishing the famous Girard-Perregaux brand, which the family acquired in 1928. Despite its history of innovation, the Mimo brand soon disappeared.

One watch comes to mind when we think of the slide rule bezel today: The Breitling Navitimer. Although Breitling is correctly credited with making the slide rule bezel famous, it was introduced with the Chronomat, not the Navitimer, and just a few months after the Mimo-Loga! Let’s set the record straight.

Most contemporary accounts claim that Breitling introduced the Chronomat in 1942, but primary sources include advertisements for “Le Chronomat” in September 1941. Although the watch may not have entered production this early, it was clearly a focus for the company at this time. Like the Mimo-Loga, the Chronomat had slide rule markings on the rotating bezel. But Breitling’s watch used a chronograph movement, and this allowed the wearer to perform many more useful calculations.

Breitling produced a companion booklet to help buyers make the most of the Chronomat’s capabilities. The dial also included red reference markings to assist in measuring seconds, fifths, minutes, and hours as well as a telemeter indicator. The Chronomat was specifically designed as a tachymeter, telemeter, pulsometer, and metronome, and the scale could perform standard mathematical calculations like previous circular slide rules. Breitling even produced a cardboard cutout model, available to retailers to help demonstrate these functions.

The Chronomat name combined these capabilities, “chronograph” and “mathematics”, but this did not last long. An automatic Chronomat without a chronograph function was introduced by 1954 and the famous Chronomatic movement further muddied the waters. Today the Chronomat line includes many chronographs but not one has a slide rule bezel.

This brings us to the most famous slide rule watch, the Breitling Navitimer. Today, the company claims that this watch was created in 1952 and released in 1954 with AOPA branding, and we have no reason to doubt their internal records. But the earliest public references to the Navitimer appear in 1955, and the trademark for the name was received on January 22 of that year. The Navitimer is a specialized watch, originally exclusively available to pilots, and may not have been publicized or even named until 1955.

While the Chronomat had indicators for various capabilities, the Navitimer was designed specifically to perform specialized calculations related to air travel: Ground speed, distance per minute, fuel consumption, rate and distance of climb or descent, and nautical and statute mile conversion. These scales and indices made for a very busy dial despite the hefty 41 mm case. Breitling’s current lineup includes a variety of beautiful and colorful interpretations of the classic Navitimer.

Incredibly, it is this specialized tool watch design that has become dominant in the public consciousness. Today there are numerous “Navitimer” style watches made by brands like Casio, Citizen, Hamilton, Seiko, and Victorinox. The Sinn 903 also deserves special mention: They bought up the remaining Navitimer stock from Breitling in 1979 and continued to sell these original watches as their Navigation Timer into the 1980s. This has remained in production today, with the Model 903 II released in March of 2024.

Rolex: Turn-o-Graph, Submariner, and GMT-Master

When the Swiss Industries Fair in Basel opened on May 8, 1954, visitors to the Rolex stand were treated to three new product releases: Explorer, Submariner, and Turn-o-Graph. These watches marked a transition for Rolex and ultimately the entire watch industry. All three were tool watches with modern Oyster cases and Perpetual movements, and two were defined by their distinctive rotating bezels.

The Turn-o-Graph name is not well-remembered today, but it was a staple of the Rolex lineup (on and off) until 2011. It was a simple time-only watch with a rotating bezel designed to calculate elapsed time. The Rolex rotating bezel was mostly flat, with a sharp knurled edge. In the Turn-o-Graph it was marked with four dots then a stick or numerals at 10, 20, 30, 40, and 50. A triangle with a luminous dot was placed at the top. This design reflected the dial, which used dots on the hour, sticks at 3, 6, and 9, and a triangle at 12, all with luminous paint. The Turn-o-Graph was thus the most harmonious of the trio.

The Submariner was very similar to the Turn-o-Graph but was rated to 200 meters. Rolex had a long history of producing waterproof watches, but the Submariner was altogether more elegant and refined. The bezel was wide and flat, lacking the dots of the Turn-o-Graph, with stick markers alternating between numerals on the 10s. Although a true icon today, this original Submariner looked like nothing else on the market at the time. The look was soon copied by the entire industry, making the simple flat rotating bezel a sports watch staple. And the Submariner is undoubtedly one of the most in-demand watches globally to this day.

On March 22, 1956, Rolex founder Hans Wilsdorf gathered friends and industry figures to the Hôtel des Bergues in Geneva to celebrate his 75th birthday and the success of the company. Along with the “Stick-o-Matic”, presented to him by the factory, the crowd was able to see a brand new Rolex model.

The GMT-Master was developed with the needs of pilots in mind, though Rolex did not go to the same extremes as the Breitling Navitimer. It was the first Rolex to feature a 24 hour hand, though it was not adjustable until the 1983 GMT-Master II. And it also included a date window under a magnifying glass bubble at 3 on the dial. But it is the rotating bezel that we will focus on, since that is the subject of this article.

Mechanically quite similar to the Submariner bezel, the GMT-Master featured alternating dots and numerals from 2 to 22, indicating the hours for the central 24 hour hand. In this way, it could be used to show the time in a second time zone by rotating the bezel ahead or behind the fixed hand. This too would become an iconic design, copied by many other firms in the coming decades. And it remains a favorite Rolex model today.

From Complex to Simple, With Many Variations

There is far more we could say about the rotating bezel, but perhaps this is enough to prove my point: Invention often proceeds from complex to simple. What was once an integrated mechanism to set the alarm or time became a simple alternate time scale. But there is subtlety to the rotating bezel! While most count up, some count down. While most are marked at 60 minute intervals, others are marked at 12. And some function as slide rules or perform complicated calculations specific to navigation. The simple bezel is far from simple, and many different companies and inventors were involved in its evolution!

The Backward Evolution of the Rotating Bezel

Not everything gets more complicated as it evolves. The bezel, once a simple frame around the glass of a watch, became an integrated mechanism before it evolved into a simple numeric scale. From alarm clocks, navigational computers, and slide rules it became the most-recognized feature of the most iconic watches. Let’s consider the history of the rotating bezel.

From Complex to Simple

We tend to think that innovation starts with simple ideas and becomes more complex over time. Surprisingly, the opposite is usually true. Lacking a clear use case, inventors tend to start with a complex concept before stripping away less-useful elements. Consider the Apple Newton, a full-featured handheld computer with dozens of innovative ideas that inspired simpler PDAs before morphing into the modern smartphone. My 2017 BMW i3 electric is truly an exotic car, built like a carbon fiber science project and entirely unlike the conventional 2027 i3 sedan.

The same is true in watchmaking, and this brings us to the humble rotating bezel. Nearly every brand has a dive watch styled after the Rolex Submariner with a bold black knurled rotating bezel marked with triangles, sticks, and numerals. Most buyers never give these a second look, let alone turn them to time a drive, let alone a dive. Some brands also make a watch styled after the Breitling Navitimer with a busy two-part bezel marked with confusing aeronautical indications of speed and fuel load. Rolex even created a functional rotating bezel for the 2012 Sky-Dweller, used to select different functions.

A bit of research reveals that the history of the humble rotating bezel runs exactly counter to expectation, beginning with functional complications before proceeding to obscure slide rules before being stripped down to a basic hour indicator. It took 50 years for the rotating bezel to be simplified enough to enter the public consciousness and that long again before Rolex invented the Sky-Dweller’s ring command. Like so many innovations, there’s a lot to learn if you look into the rotating bezel!

The Functional Bezel

The bezel itself was an innovation. Most early clocks and watches were “open faced”, but by the 17th century some included a glass to protect the dial and hands. This was mounted in a frame of metal called a bezel, which was often attached to the case with a hinge. Thus, the first bezel was a functional part of the case, if not the watch movement.

Watches in the 19th century adopted setting and winding using a crown and often had a fixed glass over the dial, since the hands no longer needed to be manually manipulated. The glass was set directly into the rounded case without a separate bezel. This gave the watch a smooth curving contour that felt in the hand like a bar of soap (“savonnette” in French). Some watches still featured a bezel around the glass, notably the screw-on bezel and back produced by Keystone and others in America.

Winding and setting functions were not unified in a single crown until the 20th century. Earlier watches often had keys for winding or were set manually by rotating the hands. Pendant winding using a crown became widespread in the 19th century, and inventors were constantly working to enable hand setting by rotating the crown as well. These often involved levers or buttons, but some involved a rotating knurled bezel very similar in concept to the modern Sky-Dweller.

As alarm watches became popular in the early 20th century, a question arose about how to set this additional function. Attention again turned to the bezel, which could be rotated to set the time of the alarm. This must have been fairly common, as 1907 coverage of a new alarm watch from F. Schweizer & Cie discusses the limitations of bezel-set alarms (reliability and accuracy).

This was notably used by Eterna on their innovative if unsuccessful 1914 Cal. 68, the first alarm wristwatch. This 13 ligne movement was offered in a small pocket watch, a wristwatch, and a convertible watch that could be mounted on the steering wheel of a car. Although the wristwatch didn’t sell well, Eterna used the same movement in a line of successful travel alarm clocks, and these inspired the entire industry to adopt this mechanism.

Soon, most alarm clocks used a rotating bezel to set the time, often with an indicator on the bezel to show the current setting. This complicated mechanism was the first widely-used rotating bezel, pre-dating the dive watch craze by three decades.

A similar system was employed by John Harwood to set the time his Perpetual, the first self-winding wristwatch. The primary driver for his invention was the need to prevent dust and moisture from damaging the movement, a common issue on the battlefields of World War I. Since sealed crowns and stems had not yet been developed, Harwood’s goal was to create a sealed case with no crown, and he was inspired by the alarm clock setting mechanism created by Eterna to use a rotating bezel to set the time.

The Harwood Perpetual was a global sensation, even if it ultimately did not find many buyers. And the knurled or fluted bezel became a common look in the 1930s, adopted by other waterproof watch cases like the Rolex Oyster. Although not a rotating bezel in the strictest sense, many of these could be unscrewed to access the hands, dial, and movement during assembly and servicing.

It is easy to see how the Harwood Perpetual inspired the legendary Rolex Oyster Perpetual, and Rolex agreed: They specifically cited Harwood along with Abraham-Louis Perrelet as inspiration for their Oyster Perpetual in a series of advertisements in the 1950s. And it wasn’t just the Perpetual name or centrally-rotating winding: Rolex popularized the rotating bezel in this same time period, introducing the Turn-o-Graph, Submariner, and GMT-Master, as we will discuss in a moment. All of these feature a bezel that strongly resembles the Harwood Perpetual.

Lindbergh, Longines, and Weems

The idea that a rotating bezel could serve as an indicator of information rather than a mechanism to set the time originates with American aviator Philip Van Horn Weems. He developed a simplified navigational system for aircraft while serving in the American Navy in the 1920s and early 1930s. His system relied on a so-called “second-setting watch” featured a rotating inner dial that could be set to a time signal over the radio. This was based on Longines’ 1918 Touran pocket watch, which was designed to be re-set to zero at sunset to approximate the Alla Turca timekeeping system of the Ottoman Empire.

A close collaboration between Weems, aviation pioneer Charles Lindburgh, Longines-Wittnauer director John P.V. Heinmuller, and the Longines and Fluckiger factories in Saint-Imier resulted in a revolutionary watch that allowed pilots to determine their location using markings on a rotating bezel. This began with a specially-modified version of the Touran watch with an outer chapter scale showing units of arc, delivered in 1930. In 1931 Longines added a rotating bezel marked with units of arc in red and green. This bezel would be pre-positioned according to the equation of time table to instantly perform the calculation needed to determine the Greenwich Hour Angle of the Sun.

Once Longines developed a stop-seconds flyback movement the inner rotating dial component was no longer needed, allowing all calculations to be performed using the rotating bezel. Later versions even dispensed with the units of arc markings on the bezel, using a simple scale with units marked 10 through 60. These were no longer Hour Angle watches at all, but they were some of the first watches with a rotating bezel. In later decades Longines produced faithful reproductions of the Lindbergh Hour Angle watch, including a lovely limited edition in 2018.

The Evolving Chronograph Bezel

As the world industrialized in the early 20th century, a need for time measurement appeared. Businesses were more interested in tracking efficiency, and aviators needed to record and note time of travel. Watchmakers struggled to develop affordable and reliable chronograph mechanisms in the 1930s and 1940s, and this a fascinating area of study. This was the era when the old monopusher gave way to the Compax, flyback, and chronostop.

The alarm time indicators of previous decades gave innovators a new idea: A rotating bezel could set an indicator to measure elapsed time. In 1935 Heuer introduced a new chronograph for aviators that featured a knurled rotating bezel attached to a white triangular indicator “to mark the departure time or any other observation.” It is unclear if this is the first chronograph watch with a rotating bezel, but it is the earliest our research has uncovered.

Breitling produced a similar-looking aviation watch with a rotating bezel in early 1936. Unlike the Heuer chronograph, the Breitling model has no minute totalizer, only chronograph seconds. As noted in Journal Suisse d’Horlogerie, the bezel indicator would “serve as the minute totalizer”, synchronized with the running minutes hand for timing flight operations.

Fortis also produced a chronostop watch with a rotating bezel in 1936. This movement had a stop and reset function for the central chronograph seconds hand using a pusher in the crown. The Fortis chronostop was the first watch we’ve seen with a full set of 60 markers on the rotating bezel, complete with numerals from 5 to 60. The design also departed from the classic rounded screw-on bezel look: It has a flat bezel that aligns with the dial along with a sharp vertical knurled edge.

The 1938 Damas Ref. 2452 dispensed with the expensive chronograph movement entirely, relying solely on a rotating bezel and central running seconds hand to record elapsed time. This watch advanced the bezel markings in a significant way: It features a triangle at the top rather than 0 or 60. This is a common design today, combining the Heuer and Breitling bezel indicator with the full minute track and vertical edge seen on the Fortis chronostop.

The next major advancement in bezel design came from Invicta, then a respected maker of complicated watches in La Chaux-de-Fonds. They introduced two models for 1940 with a deeply-grooved 12-hour bezel: The Secontrol had a chronostop movement and telemeter and tachymeter scales on the dial, while the Time-Log used a start-stop chronograph movement with three pushers. The new bezel served as an hour counter for these watches, which would be much more useful in association with the minute totalizer subdial on the Time-Log. It is unclear exactly how the 12-hour bezel would be useful on the Secontrol.

The next important advance in simple bezel design came in 1949 with the Minerva Ref. 1527, which features numerals that count down rather than up. This is useful as a reminder for future events rather than a recorder of elapsed time. Since this model is marked from 1 to 11 (again with the triangle at 12), it was designed to be used by aviators to mark the next turn using the hour hand. Count-down bezels are uncommon today but they remain an interesting variation on the theme.

The Slide Rule Bezel

The slide rule (“règle à calcul” in French) was invented by English mathematician and clergyman Reverend William Oughtred and others in the 17th century, utilizing the mathematical concept of logarithms discovered by John Napier. Logarithms exploit the relationship between two scales to perform various calculations, especially multiplication and division. Slide rules were the most convenient and accurate mathematical tool until the creation of electronic calculators and computers in the 1960s.

The straight slide rule is most familiar but the circular slide rule has existed since the 19th century. In 1905, Emile Alexandre Moret of France received a patent for a mechanical calculator that used geared hands to perform logarithmic calculations using circular disks. Moret recognized that a circular slide rule could be packaged as a clock or watch, calling his invention a “montre à calcul”, but it did not include a timekeeping function.

Zénith, the famous Le Locle watchmaking firm, received a patent for a mechanical slide rule calculator in a pocket watch case in 1918. Once again, although this resembled a watch it was actually a pocket calculator without any timekeeping capability.

Importantly, both of these designs appeared before the Harwood Perpetual watch popularized the concept of a rotating bezel. It was only a matter of time before someone moved the circular slide rule to the bezel of a watch.

Graef & Cie, Fabrique Mimo, was one of the most innovative watchmaking companies in the first half of the 20th century, introducing many firsts between 1930 and 1941: The first wristwatch with a calendar, a double-barrel 8-day movement, a digital jump-hour display, and even a quick-change strap. So it is no surprise that Mimo was also the first company to produce a wristwatch with a slide rule bezel.

The Mimo-Loga was the first watch to feature a freely-rotating bezel, and it included classic slide rule markings. The July 27, 1940 patent eloquently describes that, “in addition to the chronometric and chronograph devices, includes at least two conjugate logarithmic scales, at least one of which is mounted on a rotating member concentric with the dial that carries the other.”

The Mimo-Loga was introduced in early 1941, just before Mimo founder Otto Graef retired. He left his sons in control of Mimo to his sons, but they were more interested in re-establishing the famous Girard-Perregaux brand, which the family acquired in 1928. Despite its history of innovation, the Mimo brand soon disappeared.

One watch comes to mind when we think of the slide rule bezel today: The Breitling Navitimer. Although Breitling is correctly credited with making the slide rule bezel famous, it was introduced with the Chronomat, not the Navitimer, and just a few months after the Mimo-Loga! Let’s set the record straight.

Most contemporary accounts claim that Breitling introduced the Chronomat in 1942, but primary sources include advertisements for “Le Chronomat” in September 1941. Although the watch may not have entered production this early, it was clearly a focus for the company at this time. Like the Mimo-Loga, the Chronomat had slide rule markings on the rotating bezel. But Breitling’s watch used a chronograph movement, and this allowed the wearer to perform many more useful calculations.

Breitling produced a companion booklet to help buyers make the most of the Chronomat’s capabilities. The dial also included red reference markings to assist in measuring seconds, fifths, minutes, and hours as well as a telemeter indicator. The Chronomat was specifically designed as a tachymeter, telemeter, pulsometer, and metronome, and the scale could perform standard mathematical calculations like previous circular slide rules. Breitling even produced a cardboard cutout model, available to retailers to help demonstrate these functions.

The Chronomat name combined these capabilities, “chronograph” and “mathematics”, but this did not last long. An automatic Chronomat without a chronograph function was introduced by 1954 and the famous Chronomatic movement further muddied the waters. Today the Chronomat line includes many chronographs but not one has a slide rule bezel.

This brings us to the most famous slide rule watch, the Breitling Navitimer. Today, the company claims that this watch was created in 1952 and released in 1954 with AOPA branding, and we have no reason to doubt their internal records. But the earliest public references to the Navitimer appear in 1955, and the trademark for the name was received on January 22 of that year. The Navitimer is a specialized watch, originally exclusively available to pilots, and may not have been publicized or even named until 1955.

While the Chronomat had indicators for various capabilities, the Navitimer was designed specifically to perform specialized calculations related to air travel: Ground speed, distance per minute, fuel consumption, rate and distance of climb or descent, and nautical and statute mile conversion. These scales and indices made for a very busy dial despite the hefty 41 mm case. Breitling’s current lineup includes a variety of beautiful and colorful interpretations of the classic Navitimer.

Incredibly, it is this specialized tool watch design that has become dominant in the public consciousness. Today there are numerous “Navitimer” style watches made by brands like Casio, Citizen, Hamilton, Seiko, and Victorinox. The Sinn 903 also deserves special mention: They bought up the remaining Navitimer stock from Breitling in 1979 and continued to sell these original watches as their Navigation Timer into the 1980s. This has remained in production today, with the Model 903 II released in March of 2024.

Rolex: Turn-o-Graph, Submariner, and GMT-Master

When the Swiss Industries Fair in Basel opened on May 8, 1954, visitors to the Rolex stand were treated to three new product releases: Explorer, Submariner, and Turn-o-Graph. These watches marked a transition for Rolex and ultimately the entire watch industry. All three were tool watches with modern Oyster cases and Perpetual movements, and two were defined by their distinctive rotating bezels.

The Turn-o-Graph name is not well-remembered today, but it was a staple of the Rolex lineup (on and off) until 2011. It was a simple time-only watch with a rotating bezel designed to calculate elapsed time. The Rolex rotating bezel was mostly flat, with a sharp knurled edge. In the Turn-o-Graph it was marked with four dots then a stick or numerals at 10, 20, 30, 40, and 50. A triangle with a luminous dot was placed at the top. This design reflected the dial, which used dots on the hour, sticks at 3, 6, and 9, and a triangle at 12, all with luminous paint. The Turn-o-Graph was thus the most harmonious of the trio.

The Submariner was very similar to the Turn-o-Graph but was rated to 200 meters. Rolex had a long history of producing waterproof watches, but the Submariner was altogether more elegant and refined. The bezel was wide and flat, lacking the dots of the Turn-o-Graph, with stick markers alternating between numerals on the 10s. Although a true icon today, this original Submariner looked like nothing else on the market at the time. The look was soon copied by the entire industry, making the simple flat rotating bezel a sports watch staple. And the Submariner is undoubtedly one of the most in-demand watches globally to this day.

On March 22, 1956, Rolex founder Hans Wilsdorf gathered friends and industry figures to the Hôtel des Bergues in Geneva to celebrate his 75th birthday and the success of the company. Along with the “Stick-o-Matic”, presented to him by the factory, the crowd was able to see a brand new Rolex model.

The GMT-Master was developed with the needs of pilots in mind, though Rolex did not go to the same extremes as the Breitling Navitimer. It was the first Rolex to feature a 24 hour hand, though it was not adjustable until the 1983 GMT-Master II. And it also included a date window under a magnifying glass bubble at 3 on the dial. But it is the rotating bezel that we will focus on, since that is the subject of this article.

Mechanically quite similar to the Submariner bezel, the GMT-Master featured alternating dots and numerals from 2 to 22, indicating the hours for the central 24 hour hand. In this way, it could be used to show the time in a second time zone by rotating the bezel ahead or behind the fixed hand. This too would become an iconic design, copied by many other firms in the coming decades. And it remains a favorite Rolex model today.

From Complex to Simple, With Many Variations

There is far more we could say about the rotating bezel, but perhaps this is enough to prove my point: Invention often proceeds from complex to simple. What was once an integrated mechanism to set the alarm or time became a simple alternate time scale. But there is subtlety to the rotating bezel! While most count up, some count down. While most are marked at 60 minute intervals, others are marked at 12. And some function as slide rules or perform complicated calculations specific to navigation. The simple bezel is far from simple, and many different companies and inventors were involved in its evolution!

The Backward Evolution of the Rotating Bezel

Not everything gets more complicated as it evolves. The bezel, once a simple frame around the glass of a watch, became an integrated mechanism before it evolved into a simple numeric scale. From alarm clocks, navigational computers, and slide rules it became the most-recognized feature of the most iconic watches. Let’s consider the history of the rotating bezel.

From Complex to Simple

We tend to think that innovation starts with simple ideas and becomes more complex over time. Surprisingly, the opposite is usually true. Lacking a clear use case, inventors tend to start with a complex concept before stripping away less-useful elements. Consider the Apple Newton, a full-featured handheld computer with dozens of innovative ideas that inspired simpler PDAs before morphing into the modern smartphone. My 2017 BMW i3 electric is truly an exotic car, built like a carbon fiber science project and entirely unlike the conventional 2027 i3 sedan.

The same is true in watchmaking, and this brings us to the humble rotating bezel. Nearly every brand has a dive watch styled after the Rolex Submariner with a bold black knurled rotating bezel marked with triangles, sticks, and numerals. Most buyers never give these a second look, let alone turn them to time a drive, let alone a dive. Some brands also make a watch styled after the Breitling Navitimer with a busy two-part bezel marked with confusing aeronautical indications of speed and fuel load. Rolex even created a functional rotating bezel for the 2012 Sky-Dweller, used to select different functions.

A bit of research reveals that the history of the humble rotating bezel runs exactly counter to expectation, beginning with functional complications before proceeding to obscure slide rules before being stripped down to a basic hour indicator. It took 50 years for the rotating bezel to be simplified enough to enter the public consciousness and that long again before Rolex invented the Sky-Dweller’s ring command. Like so many innovations, there’s a lot to learn if you look into the rotating bezel!

The Functional Bezel

The bezel itself was an innovation. Most early clocks and watches were “open faced”, but by the 17th century some included a glass to protect the dial and hands. This was mounted in a frame of metal called a bezel, which was often attached to the case with a hinge. Thus, the first bezel was a functional part of the case, if not the watch movement.

Watches in the 19th century adopted setting and winding using a crown and often had a fixed glass over the dial, since the hands no longer needed to be manually manipulated. The glass was set directly into the rounded case without a separate bezel. This gave the watch a smooth curving contour that felt in the hand like a bar of soap (“savonnette” in French). Some watches still featured a bezel around the glass, notably the screw-on bezel and back produced by Keystone and others in America.

Winding and setting functions were not unified in a single crown until the 20th century. Earlier watches often had keys for winding or were set manually by rotating the hands. Pendant winding using a crown became widespread in the 19th century, and inventors were constantly working to enable hand setting by rotating the crown as well. These often involved levers or buttons, but some involved a rotating knurled bezel very similar in concept to the modern Sky-Dweller.

As alarm watches became popular in the early 20th century, a question arose about how to set this additional function. Attention again turned to the bezel, which could be rotated to set the time of the alarm. This must have been fairly common, as 1907 coverage of a new alarm watch from F. Schweizer & Cie discusses the limitations of bezel-set alarms (reliability and accuracy).

This was notably used by Eterna on their innovative if unsuccessful 1914 Cal. 68, the first alarm wristwatch. This 13 ligne movement was offered in a small pocket watch, a wristwatch, and a convertible watch that could be mounted on the steering wheel of a car. Although the wristwatch didn’t sell well, Eterna used the same movement in a line of successful travel alarm clocks, and these inspired the entire industry to adopt this mechanism.

Soon, most alarm clocks used a rotating bezel to set the time, often with an indicator on the bezel to show the current setting. This complicated mechanism was the first widely-used rotating bezel, pre-dating the dive watch craze by three decades.

A similar system was employed by John Harwood to set the time his Perpetual, the first self-winding wristwatch. The primary driver for his invention was the need to prevent dust and moisture from damaging the movement, a common issue on the battlefields of World War I. Since sealed crowns and stems had not yet been developed, Harwood’s goal was to create a sealed case with no crown, and he was inspired by the alarm clock setting mechanism created by Eterna to use a rotating bezel to set the time.

The Harwood Perpetual was a global sensation, even if it ultimately did not find many buyers. And the knurled or fluted bezel became a common look in the 1930s, adopted by other waterproof watch cases like the Rolex Oyster. Although not a rotating bezel in the strictest sense, many of these could be unscrewed to access the hands, dial, and movement during assembly and servicing.

It is easy to see how the Harwood Perpetual inspired the legendary Rolex Oyster Perpetual, and Rolex agreed: They specifically cited Harwood along with Abraham-Louis Perrelet as inspiration for their Oyster Perpetual in a series of advertisements in the 1950s. And it wasn’t just the Perpetual name or centrally-rotating winding: Rolex popularized the rotating bezel in this same time period, introducing the Turn-o-Graph, Submariner, and GMT-Master, as we will discuss in a moment. All of these feature a bezel that strongly resembles the Harwood Perpetual.

Lindbergh, Longines, and Weems

The idea that a rotating bezel could serve as an indicator of information rather than a mechanism to set the time originates with American aviator Philip Van Horn Weems. He developed a simplified navigational system for aircraft while serving in the American Navy in the 1920s and early 1930s. His system relied on a so-called “second-setting watch” featured a rotating inner dial that could be set to a time signal over the radio. This was based on Longines’ 1918 Touran pocket watch, which was designed to be re-set to zero at sunset to approximate the Alla Turca timekeeping system of the Ottoman Empire.

A close collaboration between Weems, aviation pioneer Charles Lindburgh, Longines-Wittnauer director John P.V. Heinmuller, and the Longines and Fluckiger factories in Saint-Imier resulted in a revolutionary watch that allowed pilots to determine their location using markings on a rotating bezel. This began with a specially-modified version of the Touran watch with an outer chapter scale showing units of arc, delivered in 1930. In 1931 Longines added a rotating bezel marked with units of arc in red and green. This bezel would be pre-positioned according to the equation of time table to instantly perform the calculation needed to determine the Greenwich Hour Angle of the Sun.

Once Longines developed a stop-seconds flyback movement the inner rotating dial component was no longer needed, allowing all calculations to be performed using the rotating bezel. Later versions even dispensed with the units of arc markings on the bezel, using a simple scale with units marked 10 through 60. These were no longer Hour Angle watches at all, but they were some of the first watches with a rotating bezel. In later decades Longines produced faithful reproductions of the Lindbergh Hour Angle watch, including a lovely limited edition in 2018.

The Evolving Chronograph Bezel

As the world industrialized in the early 20th century, a need for time measurement appeared. Businesses were more interested in tracking efficiency, and aviators needed to record and note time of travel. Watchmakers struggled to develop affordable and reliable chronograph mechanisms in the 1930s and 1940s, and this a fascinating area of study. This was the era when the old monopusher gave way to the Compax, flyback, and chronostop.

The alarm time indicators of previous decades gave innovators a new idea: A rotating bezel could set an indicator to measure elapsed time. In 1935 Heuer introduced a new chronograph for aviators that featured a knurled rotating bezel attached to a white triangular indicator “to mark the departure time or any other observation.” It is unclear if this is the first chronograph watch with a rotating bezel, but it is the earliest our research has uncovered.

Breitling produced a similar-looking aviation watch with a rotating bezel in early 1936. Unlike the Heuer chronograph, the Breitling model has no minute totalizer, only chronograph seconds. As noted in Journal Suisse d’Horlogerie, the bezel indicator would “serve as the minute totalizer”, synchronized with the running minutes hand for timing flight operations.

Fortis also produced a chronostop watch with a rotating bezel in 1936. This movement had a stop and reset function for the central chronograph seconds hand using a pusher in the crown. The Fortis chronostop was the first watch we’ve seen with a full set of 60 markers on the rotating bezel, complete with numerals from 5 to 60. The design also departed from the classic rounded screw-on bezel look: It has a flat bezel that aligns with the dial along with a sharp vertical knurled edge.

The 1938 Damas Ref. 2452 dispensed with the expensive chronograph movement entirely, relying solely on a rotating bezel and central running seconds hand to record elapsed time. This watch advanced the bezel markings in a significant way: It features a triangle at the top rather than 0 or 60. This is a common design today, combining the Heuer and Breitling bezel indicator with the full minute track and vertical edge seen on the Fortis chronostop.

The next major advancement in bezel design came from Invicta, then a respected maker of complicated watches in La Chaux-de-Fonds. They introduced two models for 1940 with a deeply-grooved 12-hour bezel: The Secontrol had a chronostop movement and telemeter and tachymeter scales on the dial, while the Time-Log used a start-stop chronograph movement with three pushers. The new bezel served as an hour counter for these watches, which would be much more useful in association with the minute totalizer subdial on the Time-Log. It is unclear exactly how the 12-hour bezel would be useful on the Secontrol.

The next important advance in simple bezel design came in 1949 with the Minerva Ref. 1527, which features numerals that count down rather than up. This is useful as a reminder for future events rather than a recorder of elapsed time. Since this model is marked from 1 to 11 (again with the triangle at 12), it was designed to be used by aviators to mark the next turn using the hour hand. Count-down bezels are uncommon today but they remain an interesting variation on the theme.

The Slide Rule Bezel

The slide rule (“règle à calcul” in French) was invented by English mathematician and clergyman Reverend William Oughtred and others in the 17th century, utilizing the mathematical concept of logarithms discovered by John Napier. Logarithms exploit the relationship between two scales to perform various calculations, especially multiplication and division. Slide rules were the most convenient and accurate mathematical tool until the creation of electronic calculators and computers in the 1960s.

The straight slide rule is most familiar but the circular slide rule has existed since the 19th century. In 1905, Emile Alexandre Moret of France received a patent for a mechanical calculator that used geared hands to perform logarithmic calculations using circular disks. Moret recognized that a circular slide rule could be packaged as a clock or watch, calling his invention a “montre à calcul”, but it did not include a timekeeping function.

Zénith, the famous Le Locle watchmaking firm, received a patent for a mechanical slide rule calculator in a pocket watch case in 1918. Once again, although this resembled a watch it was actually a pocket calculator without any timekeeping capability.

Importantly, both of these designs appeared before the Harwood Perpetual watch popularized the concept of a rotating bezel. It was only a matter of time before someone moved the circular slide rule to the bezel of a watch.

Graef & Cie, Fabrique Mimo, was one of the most innovative watchmaking companies in the first half of the 20th century, introducing many firsts between 1930 and 1941: The first wristwatch with a calendar, a double-barrel 8-day movement, a digital jump-hour display, and even a quick-change strap. So it is no surprise that Mimo was also the first company to produce a wristwatch with a slide rule bezel.

The Mimo-Loga was the first watch to feature a freely-rotating bezel, and it included classic slide rule markings. The July 27, 1940 patent eloquently describes that, “in addition to the chronometric and chronograph devices, includes at least two conjugate logarithmic scales, at least one of which is mounted on a rotating member concentric with the dial that carries the other.”

The Mimo-Loga was introduced in early 1941, just before Mimo founder Otto Graef retired. He left his sons in control of Mimo to his sons, but they were more interested in re-establishing the famous Girard-Perregaux brand, which the family acquired in 1928. Despite its history of innovation, the Mimo brand soon disappeared.

One watch comes to mind when we think of the slide rule bezel today: The Breitling Navitimer. Although Breitling is correctly credited with making the slide rule bezel famous, it was introduced with the Chronomat, not the Navitimer, and just a few months after the Mimo-Loga! Let’s set the record straight.

Most contemporary accounts claim that Breitling introduced the Chronomat in 1942, but primary sources include advertisements for “Le Chronomat” in September 1941. Although the watch may not have entered production this early, it was clearly a focus for the company at this time. Like the Mimo-Loga, the Chronomat had slide rule markings on the rotating bezel. But Breitling’s watch used a chronograph movement, and this allowed the wearer to perform many more useful calculations.

Breitling produced a companion booklet to help buyers make the most of the Chronomat’s capabilities. The dial also included red reference markings to assist in measuring seconds, fifths, minutes, and hours as well as a telemeter indicator. The Chronomat was specifically designed as a tachymeter, telemeter, pulsometer, and metronome, and the scale could perform standard mathematical calculations like previous circular slide rules. Breitling even produced a cardboard cutout model, available to retailers to help demonstrate these functions.

The Chronomat name combined these capabilities, “chronograph” and “mathematics”, but this did not last long. An automatic Chronomat without a chronograph function was introduced by 1954 and the famous Chronomatic movement further muddied the waters. Today the Chronomat line includes many chronographs but not one has a slide rule bezel.

This brings us to the most famous slide rule watch, the Breitling Navitimer. Today, the company claims that this watch was created in 1952 and released in 1954 with AOPA branding, and we have no reason to doubt their internal records. But the earliest public references to the Navitimer appear in 1955, and the trademark for the name was received on January 22 of that year. The Navitimer is a specialized watch, originally exclusively available to pilots, and may not have been publicized or even named until 1955.

While the Chronomat had indicators for various capabilities, the Navitimer was designed specifically to perform specialized calculations related to air travel: Ground speed, distance per minute, fuel consumption, rate and distance of climb or descent, and nautical and statute mile conversion. These scales and indices made for a very busy dial despite the hefty 41 mm case. Breitling’s current lineup includes a variety of beautiful and colorful interpretations of the classic Navitimer.

Incredibly, it is this specialized tool watch design that has become dominant in the public consciousness. Today there are numerous “Navitimer” style watches made by brands like Casio, Citizen, Hamilton, Seiko, and Victorinox. The Sinn 903 also deserves special mention: They bought up the remaining Navitimer stock from Breitling in 1979 and continued to sell these original watches as their Navigation Timer into the 1980s. This has remained in production today, with the Model 903 II released in March of 2024.

Rolex: Turn-o-Graph, Submariner, and GMT-Master

When the Swiss Industries Fair in Basel opened on May 8, 1954, visitors to the Rolex stand were treated to three new product releases: Explorer, Submariner, and Turn-o-Graph. These watches marked a transition for Rolex and ultimately the entire watch industry. All three were tool watches with modern Oyster cases and Perpetual movements, and two were defined by their distinctive rotating bezels.

The Turn-o-Graph name is not well-remembered today, but it was a staple of the Rolex lineup (on and off) until 2011. It was a simple time-only watch with a rotating bezel designed to calculate elapsed time. The Rolex rotating bezel was mostly flat, with a sharp knurled edge. In the Turn-o-Graph it was marked with four dots then a stick or numerals at 10, 20, 30, 40, and 50. A triangle with a luminous dot was placed at the top. This design reflected the dial, which used dots on the hour, sticks at 3, 6, and 9, and a triangle at 12, all with luminous paint. The Turn-o-Graph was thus the most harmonious of the trio.

The Submariner was very similar to the Turn-o-Graph but was rated to 200 meters. Rolex had a long history of producing waterproof watches, but the Submariner was altogether more elegant and refined. The bezel was wide and flat, lacking the dots of the Turn-o-Graph, with stick markers alternating between numerals on the 10s. Although a true icon today, this original Submariner looked like nothing else on the market at the time. The look was soon copied by the entire industry, making the simple flat rotating bezel a sports watch staple. And the Submariner is undoubtedly one of the most in-demand watches globally to this day.

On March 22, 1956, Rolex founder Hans Wilsdorf gathered friends and industry figures to the Hôtel des Bergues in Geneva to celebrate his 75th birthday and the success of the company. Along with the “Stick-o-Matic”, presented to him by the factory, the crowd was able to see a brand new Rolex model.

The GMT-Master was developed with the needs of pilots in mind, though Rolex did not go to the same extremes as the Breitling Navitimer. It was the first Rolex to feature a 24 hour hand, though it was not adjustable until the 1983 GMT-Master II. And it also included a date window under a magnifying glass bubble at 3 on the dial. But it is the rotating bezel that we will focus on, since that is the subject of this article.

Mechanically quite similar to the Submariner bezel, the GMT-Master featured alternating dots and numerals from 2 to 22, indicating the hours for the central 24 hour hand. In this way, it could be used to show the time in a second time zone by rotating the bezel ahead or behind the fixed hand. This too would become an iconic design, copied by many other firms in the coming decades. And it remains a favorite Rolex model today.

From Complex to Simple, With Many Variations

There is far more we could say about the rotating bezel, but perhaps this is enough to prove my point: Invention often proceeds from complex to simple. What was once an integrated mechanism to set the alarm or time became a simple alternate time scale. But there is subtlety to the rotating bezel! While most count up, some count down. While most are marked at 60 minute intervals, others are marked at 12. And some function as slide rules or perform complicated calculations specific to navigation. The simple bezel is far from simple, and many different companies and inventors were involved in its evolution!

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