|Brand:||Daini Seikosha, Seiko|
|Winding:||Automatic, Bi-Directional Automatic Winding|
|Complications:||Date, Day, Hacking Seconds, Hand Winding, Quick Date Correction, Quick Day Correction|
|Hands:||Central Hour Hand, Central Minute Hand, Central Seconds Hand, Date Window at 3:00, Day Window at 3:00|
|Distinguishing Technical Characteristics|
Clockwise Balance Cock
|Production: 1972 – 1973|
Cal. 5246A is an automatic chronometer movement with day and date produced by Daini Seikosha for use in Seiko Vanac and King Seiko watches from 1972 through 1973. It was similar to the contemporary Cal. 5206A and was superseded by the similar Cal. 5256A, which had an improved spring-loaded date quickset pawl.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.
One novel feature of some 52 stream movements was a micro-adjuster screw located at 6:30. This pushed a pivot that allowed the balance to be adjusted through the case, rather than using the “tadpole” adjuster seen on other movements. These movements also feature a lever below the 4:00 marker on the dial to release the winding stem.
This feature, which Seiko refers to in service documents as “outside micro-adjusting device,” is found is seen on some watches with Cal. 5245A and 5246A with solid “monocoque” cases. Examples of these include the King Seiko 5245-6000 and 5246-6000.
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.