The Seiko 6601A is a mechanical watch movement with various notable features such as Seiko-Diafix combined settings for the escape wheel and 3rd wheel, a ball-bearing rotor, and a sophisticated excenter self-winding mechanism with just one gear stage. Its functions include automatic winding, sweep seconds, a day display with settings in 2 languages using a pusher at 2 o'clock, and a quickset date feature. This movement was commonly used around 1975.