Cal. 5256A is an automatic chronometer movement with day and date produced by Daini Seikosha for use in Seiko Vanac and King Seiko watches from 1973 through 1976. It was similar to the contemporary Cal. 5216A and superseded the similar Cal. 5246A, which lacked its improved spring-loaded date quickset pawl. It is part of the short-lived Daini Seikosha 52 stream that powered Vanac, Special, and Chronometer watches in the classic period and was the foundation for the updated Seiko 4S series that powered most high-end mechanical watches from Seiko in the 1990s.
This was a modern movement with bi-directional automatic winding (using a conventional reverser rather than Seiko’s Magic Lever technology), hacking seconds, hand winding capability, quickset day and date using the crown, and a bilingual day wheel. It operated at 8 Hz (28,800 A/h), considered “Hi-Beat” at the time, and was capable of high levels of accuracy. The movement measured 25.60 mm in diameter and was 3.95 mm thick. A “tadpole” style micro adjuster was used, along with Diashock anti-shock and Diafix oil lubrication.
Because it was just the second automatic movement family designed by Daini Seikosha, the 52 stream had some quirks. Notably, the hand winding mechanism remains engaged when setting the date, causing drag on the crown. The date pawl on Cal. 5206A and 5246A was also prone to breakage when the watch was adjusted near midnight. This was fixed in the similar Cal. 5216A and 5256A, which replaced these movements in 1972 and 1973.
Daini Seikosha 52 Stream Family
| Date Only | Day-Date | |
|---|---|---|
| Standard | Cal. 5206A Cal. 5216A | |
| Special | Cal. 5245A | Cal. 5246A Cal. 5256A |