Note: I'm fairly new on this forum and my native language is Dutch. Please let me know if I can improve something. I've searched on the web and found the history stated as below. If there're any false statements, please let me know! Recently I came across a Girard-Perregaux - Gyromatic: The watch: This is a Girard-Perregaux Gyromatic ref. 7317 from around 1958. This model houses a caliber 21, 18.000 vph, with 39 jewels. With a diameter of 34mm and lugsize of 18mm it wears very comfortable. Unfortunately the crown isn't original anymore, but the case seems in good condition. The dial is difficult to capture, has a nice radium burn, applied indices and a very nice blue date wheel. I wasn't familiar with a "Gyromatic", so I started to read something about it. On different sites are different bits and pieces written about this model. I'll try to combine the essence of those bits an pieces to explain what the Gyromatic is. The photos of advertisements used below are from Blomman (link: https://www.watchprozine.com/girard...girard-perregaux-gyromatic-39-jewels/8295043/ ) The other photos of the watch are my own. History: Girard-Perregaux started to make the Gyromatic model in 1957. The Gyromatic is a roller-bearing and rotation inverse mechanisme built into automatic watches. This makes the watch bi-directional winding and was supposed to improve winding the watch automatically. The jeweled roller-bearings are between the rotor and the mainspring and reduce friction. I tried to capture those jewel-rollers on a macro shot, one of which is visible above the balance wheel, the other is closed on the other left side of the bridge. According to the advertisements in 1957: "The Gyrotronic is the invention of a Swiss horological engineer and represents an entirely new solution to an age-old technical problem. It combines with almost incredible simplicity such intricate functions as: Roller-Bearing, Free-Wheel, Automatic Clutch and Rotation-Inverser." "The Gyromatic transmits energy of every movement to the mainspring without any loss. The very first milligramme of energy automatically pinches the rollers of ruby transmitting that energy to the mainspring." They even state: "The scarcely perceptible movements of a person aspeel suffice to wind up the watch automatically." Quite a statement if you ask me. Besides the lovely advertisements, I've also came across a commercial, very confusing but very vintage way of advertising dating 1958: Girard-Perregaux writes the following on their own website about the Gyromatic: “In 1957, the watchmakers of the Manufacture introduced the Gyromatic, an ultra-thin high-performance automatic winding system enabling the production of remarkably thin watches. This principle reached its peak in 1965 in equipping the world’s first ever high-frequency mechanical self-winding movement, the Gyromatic HF, beating at a rate of 36,000 vibrations per hour. “ (source: https://www.girard-perregaux.com/en/heritage-duty ) My Gyromatic with cal. 21runs only at 18.000 vph, still a pretty watch though Fratello Watches also wrote a nice article about the Gyromatic. This article has it focus on the High-frequency cal 32a, but also writes some information about the other models in the Gyromatic line. And has a very nice picture of the mechanism, but a bit blurry. (source: https://www.fratellowatches.com/ins...rregaux-gyromatic-chronometer-hf-calibre-32a/ ) A couple of years ago Girard-Perregaux launched a tribute to the Gyromatic watch, see article from Monochrome Watches in the link below. The Girard-Perregaux 1957 “Tribute to the Gyromatic”, equipped with the cal. GP03300-0130, providing 46h power reserve, ticking at 28.800 vph. And... This automatic watch has 27 jewels. Retailprice in 2016: 10,400 Swiss Francs / 10,300 USD. It sure is a beauty. (Source: https://monochrome-watches.com/gira...ute-gyromatic-really-live-photos-specs-price/ ) Girard-Perregaux-1957-tribute-to-Gyromatic-7.jpg Jewel counting: So 14 of the 39 jewels are functioning as a roller bearing between the rotor and mainspring. That leaves 25 jewels in the rest of the movement. I really appreciate the topic of @ulackfocus here on OF where he explains some history of the jewels: "Before rubies could be synthesized, only the most costly watches had more than 7 jewels. After that time, it became a marketing game of who had the most since the general public was not aware of the lower price of synthetic gems" "There were no regulations on jewels until 1965 when the NIHS (Normes de l'Industrie Horlogie Suisse) stepped in to police the advertising. ... The NIHS also defined what functioning and non-functioning jewels are in ISO 1112. The former is a "jewel which serves to stabilize friction and to reduce the wear rate of contacting surfaces of the components of a timekeeping instrument". ... As with most laws there are loopholes. Some manufacturers add jewels where they do have a tiny function but are practically useless and don't improve accuracy, reduce much friction or add to the life expectancy of the unit." (Link for those who haven't read it: https://omegaforums.net/threads/horology-101-jewels-part-1.76575/ , and another recommended article about too many jewels: https://web.archive.org/web/20080702024820/http://www.timezone.com/library/workbench/workbench0025 ) So, are those extra 14 jewels, functioning jewels? For me, this is unclear. My guess would be that those 14 jewels are non-functioning jewels. I suppose that this is the case seeing GP doesn't produces 39 jeweled calibers and even their tribute to the Gyromatic has "only" 27 jewels. I don't think these jewels improve accuracy, reduce much friction or add to the life expectancy of the watch. But.. an automatic watch has the highest accuracy when fully wound. The mainspring drives the watch and a constant force would increase accuracy. So if this Gyromatic mechanism would improve the winding it would theoretically add to the accuracy of the watch, right? Sidenote: To my surprise there's an interesting article on Wikipedia explaining the positions of the jewels: https://en.m.wikipedia.org/wiki/Mechanical_watch . Some photo's of old advertisements: This advertisement above does look a lot like mine, doesn't it? And some photo's of my own: Conclusion: The Gyromatic is a mechanism where jewels function as a bear roller between the rotor and the mainspring. This mechanism makes it bi-directional winding and was supposed to improve the winging of the mainspring. Since NIHS rules in 1965 on what "functional jewels" are, GP didn't make 39 jeweled Gyromatic. Still, GP claims that the later Gyromatic with cal 32a was the first HF automatic caliber. In 2016 GP launched a tribute to the Gyromatic, with 2 jewels, but in the same style. I've worn a Gyromatic for the last week. It wears comfortable on the wrist, I love the dial and the blue date. The applied indices are a real light catcher. I don't notice the Gyromatic mechanism winding the watch more efficiently than other watches I wear. But I like the idea of this mechanism!