The Citizen 8100A is a manual wind watch movement that was produced in low volumes starting from 1963, primarily for De Luxe models. It offers the option of a date hand, and the minute wheel is uniquely placed aside the barrel, driven by an intermediate wheel, allowing for a thinner design compared to contemporary movements. The winding energy is transferred to the barrel through a series of intermediate wheels, resulting in a compact and stable layout. In addition, the movement features an independently wound barrel that can be operated by hand or automatically. It also includes functions such as automatic winding, sweep second hand, and a date setting mechanism from 21:30 to 24h.