The A Michel 505 watch movement is an open-face calibre with a Breguet hairspring. It features variations in height and stem mechanisms, even offering a larger diameter option suitable for US cases. The movements are marked with their diameter in lignes and height in 1/12 lignes, or a newer 3-digit designation. The A Michel 505 movement offers functions such as stem winding and setting, as well as a sub-second display. It was commonly used around the 1940s.