The Citizen 1800 is an open face calibre watch movement featuring a Breguet hairspring and a negative stem mechanism specifically designed for the US market. It is worth noting that movements with the same base plate and bridge layouts were manufactured in various heights and stem mechanisms, with some even having a larger diameter to accommodate US cases. These movements are typically marked with their diameter in lignes and height in 1/12 lignes, or with a newer three-digit designation. In terms of functions, the Citizen 1800 offers stem winding and setting, as well as a sub-second feature.