|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.
Quick date correction is accomplished with the crown pulled out in second position, rotating counter-clockwise.
|Spron 510 Mainspring|
NH71A (skeleton, gilt)
|Day and Date||4R36A|
|Date, 24 Hour Subdial||4R37A|
|24 Hour Subdial||4R39A|
|Date by Pointer|