The Fontainemelon 261 is an open face calibre watch movement featuring a pin-lever escapement. It incorporates a ratchet on the dial side and a hidden crown mechanism with a rocker bar. The movement is built on a two-layer base plate. The specific differences between the 146B/15 and 146C/15 are unknown. The functions of the movement include stem winding and setting, as well as featuring a sub-second display. It was commonly used during the approximate period of 1960.