The Seiko 4006A watch movement features a jewel-bearing rotor and a sophisticated excenter self-winding mechanism with just one gear stage. It is equipped with an easy-to-operate rotor lock. Early samples of the movement utilized a slip spring, while late samples incorporated a fixed mainspring and a friction clutch on the pawl wheel. The movement offers various functions, including automatic winding and sweep seconds. It was primarily used during the approximate period of 1955.