(Not necessarily those very gears but gears typically used in watches.)
I have experience cutting 0.3mm and 0.1mm brass. The second is just wobbling everywhere like a reed in the wind, while those gears seems to be solid.
I had extremely limited success replicating a gear using a 0.3mm FDM Cartesian 3d printer, but even then I had to manually shave off every single tooth under a loupe.
Accutron is where the really small engineering comes in: https://www.youtube.com/watch?v=XugX5zb1rG8 the wheel is about 25mm across (I think) but you can't really see the teeth with the naked eye. (https://www.watchdoctor.biz/accutron/ has more details) but the level of accuracy and detail needed to machine that far outweighs the stuff that rolex do even now.
These index wheels were mass produced, and I still don't know how they did it.
> These index wheels were mass produced, and I still don't know how they did it.
Fascinating. My guess would be some form of etching process. But that would make it some form of MEMS years before the first commonly recognised MEMS components.