The ETA 2640 watch movement is a mechanical movement with various bridge shapes. Due to limited information, the exact differences between the different variations of this movement, including models 1, 2, 30, 31, 50, 65 old, 66 old, 70 old, 71 old, 73 old, 76 old, 78, 90, 91, 107, 108, 110, and 112, are not known. This movement is manually wound and features a sub-second function. It was commonly used around the 1940s.