The Felsa 337 watch movement is a manual wind movement that was in use from 1959 to 1970. It features a Breguet hairspring and a non-stop variant for Ermetoscope models, which allows for winding by closing the slide case. This variant includes a special stem with gear and a barrel with friction clutch. The movement includes a sweep second hand and a date function that can be set within a range of +/- 24 hours.