The Miyota 8205 watch movement is an automatic movement with a ball-bearing rotor and two roller freewheels. It features a worm screw regulation gear and is based on the manual wind calibre AS 1687/1688. Developed in collaboration with Doxa, Eberhard, Favre-Leuba, Girard-Perregaux, and Zodiac, the specific differences between the 42.0, 42.1, and 42.4 are not known. The movement includes functions such as automatic winding, sweep seconds, a date feature set by changing the 20:40-24h, and a hack feature. It was commonly used during the period of approximately 1970.