The Seiko 6105A watch movement is equipped with a pin-lever escapement and incorporates a calendar as a module on the M31 base. It features a sophisticated excenter self-winding mechanism that utilizes just one gear stage. A lever, moved by an excenter on the rotor arbor, engages with a ratchet wheel through two clicks. On the dial side, a planet differential gear conveys the combined power from both automatic and manual winding through two planet wheels, effectively enabling different gear ratios and complete decoupling of both winding sources. Additional functions of the Seiko 6105A include automatic winding, sweep second hand, day display, and a date feature that can be set by changing the time to 18:50-24h. This movement was commonly used around 1974.