The Cupillard 256-11 watch movement, also known as Omega 42.7 after its renaming in 1919, is an open-face calibre movement that was produced from 1911 to 1919. It features a bimetallic screw balance, which is adjustable through four adjustment screws, and uses a Breguet hairspring. Additionally, it is equipped with a negative stem mechanism specifically designed for the US market. This movement includes the following functions: stem winding and setting, as well as a sub-second display.