The A. Schild 664 watch movement is a manual wind mechanical movement that features a bimetallic screw balance and a Breguet hairspring. It was introduced in 1934 and is part of a series of redesigns known as T1, T2, and T3, with specific differences between them not disclosed. The initial version, the 23.7S, had distinct variations in dial mounting, click- and crown mechanisms. The movement includes a sub-second function.