|Brand:||Seiko, Seiko Instruments Inc., Time Module Inc.|
|Winding:||Automatic, Bi-Directional Automatic Winding|
|Diameter:||27.40 mm (12 ligne)|
|Complications:||Date, Quick Date Correction|
|Hands:||Central Hour Hand, Central Minute Hand, Central Seconds Hand, Date Window at 3:00|
|Production: 2008 – Current|
Seiko Cal. 4R15A (commonly called just Cal. 4R15) is an automatic movement with date wheel. It was later updated as Cal. 4R15B and is closely related to Cal. 4R16A/4R16B. It is also offered by Time Module Inc. (TMI) as Cal. NH15A with 21 jewels for use by other watch makers. It was the first of a new generation of movements based on the Seiko 7S family and uses a high-spec Spron 510 mainspring as in the related Seiko 6R family for greater than 50 hours running time. Later members of the Seiko 4R family included hacking seconds and hand-winding, but this is not present in the 4R15 or 4R16.
The movement can be manually wound with the crown in position 1. Rotate the crown clockwise to wind the mainspring.
The date wheel is advanced with the crown in second position (one notch out). Turn the crown counter-clockwise to advance the date wheel by one day.
The time is set with the crown in third position (pulled all the way out). Rotate the crown clockwise to advance the minute and hour hands and counter-clockwise to turn them backward.
|Spron 510 Mainspring|
NH71A (skeleton, gilt)
|Day and Date||4R36A|
|Date, 24 Hour Subdial||4R37A|
|24 Hour Subdial||4R39A|
|Date by Pointer|