Calibre 2236 Is fitted which has a Syloxi hairspring that is produced by Rolex and patented. This silicon hairspring features a patented geometry that assures the calibre’s regularity in almost any posture. The third big phase took place in the early 1900’s. The shape from the timekeeping apparatus modified in https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/