The Fontainemelon 36-21 watch movement is an open face calibre available in 18.5 and 19''' sizes. It has a height of 4.2, 5.0, or 5.9mm and offers options such as a bimetallic screw balance and Breguet hairspring. There are different bridge layouts, two base plates with varying dial-feet positions, and slightly different setting-lever springs. The assignment of these differences to groups FHF 1 to 14 and the calibres FHF 1144, 2144, 2146, 4144, 4146 is only partially known. The movement groups, designated as FHF 1 to FHF 16, encompass calibres of different dimensions, with individual designations starting at FHF 22. It features stem winding and setting, a sub-second function, and was commonly used around 1940.