|Brand:||Seiko, Seiko Instruments Inc.|
|Reserve:||40, 41 hours|
|Winding:||Automatic, Bi-Directional Automatic Winding|
|Diameter:||27.40 mm (12 ligne)|
|Complications:||Hacking Seconds, Hand Winding|
|Hands:||Central Hour Hand, Central Minute Hand, Central Seconds Hand, Open Heart at 9:00|
|Production: – Current|
Seiko Cal. 4R38A (commonly called just Cal. 4R38) is a mainstream automatic movement with open heart balance at 9:00. It is also offered by Time Module Inc. (TMI) as Cal. NH38A for use by other watch makers. It is closely related to the date-only Cal. 4R35 and the Cal. 4R37 and 4R39, both of which have a 24 hour subdial at 10:00.
It is also used in the Seiko Original line, where the company specifies accuracy to -35/+45 seconds per day and 41 hours power reserve.
Hand winding is accomplished with the crown in first position, rotating clockwise.
|Spron 510 Mainspring|
NH71A (skeleton, gilt)
|Day and Date||4R36A|
|Date, 24 Hour Subdial||4R37A|
|24 Hour Subdial||4R39A|
|Date by Pointer|