The A Michel 491 watch movement was produced from 1937 to 1970, with a total production of over 3.5 million units. It featured various chrono mechanisms, and its parts were often interchangeable, leading to the occasional combination of parts from different calibers. The A Michel 491, 151, and modified parts were also compatible with minor differences. The movement included functions such as a manual-wind chronograph with a 60-second measurement capability, a subsecond display, and a switchable cam for 30/45-minute timing intervals.