The Baume & Mercier 12820 is a mechanical watch movement that was in use from 1958 to 1963. It features a flat freesprung hairspring and a DuraBalance regulator with two regulating weights. The balance settings are combined, and shock protection is provided by the elastical balance spokes. The movement has an indirectly driven minute hand, allowing for a larger balance and a sturdy rotor bearing. It is an automatic movement with two roller freewheels stacked on the rotor hub. Notably, the ratchet is only present in the selfwinding gear, and the crown mechanism includes a rocker bar. In addition, the movement incorporates the functions of automatic winding and a sweep second hand.