The Elgin 556 mechanical watch movement is a manual wind movement with a sub second function. It belongs to the ETA 360 series, which includes the 361, 362, 364, 365, 366, and 367 movements. It shares similarities with the ETA 500, 501, and 505-509 movements, although the specific differences are not known. The Elgin 556 movement was commonly used in watches around the year 1925.