The Citizen 1805 is a mechanical watch movement featuring a pin lever escapement. It incorporates a ratchet on the dial side and a crown mechanism with a rocker bar. The 051/04 is part of a series that includes the 051/01, 051/03, 051/03a, 051/04, 051/04a, and 051/04e, with only minor differences between them. The movement offers manual winding capabilities and includes a sub-second function. Its period of use can be traced back to approximately 1955.