The Zenith 4001 watch movement, developed during the period of 1948 onwards, is notable for being the first automatic movement with a ball-bearing rotor. Early samples of the movement featured a rotor shape that differed from subsequent versions. It is worth mentioning that the Zenith 4001 movement is comparable to the ETA family 1216-1218 in terms of functionalities, albeit lacking a ball bearing mechanism. This movement incorporates several features, including an automatic winding system and a sweep second function.