The A Michel 504 is an open face calibre pocket watch movement. It offers options of a bimetallic screw balance and a Breguet hairspring. This movement comes in various sizes, including 18.5 und 19''', with heights ranging from 4.2mm to 5.9mm. It features different bridge layouts, two base plates with varying dial-feet positions, and two slightly differing setting-lever springs. The assignment of these differences to specific groups and calibres is partially known. Comparing the related calibres provides insights into their similarities and variations. The A Michel 504 movement combines functions like stem wind and set, sub second, and was commonly used during the period around 1940.