The Fontainemelon 21 watch movement, with a hunter calibre design, is believed to potentially share certain parts including the balance and keyless works with calibres 763, 790-793, 4, 5, 8, 9, 15, 954, 955, and 2709. However, due to the limited documentation and absence of visual references for these calibres, these connections remain uncertain. The movement is known to feature stem winding and setting, as well as a sub-second function. Its production period is estimated to be around the 1930s.