Seiko Cal. 4R36A is a mainstream automatic movement with day and date wheels. It is also offered by Time Module Inc. (TMI) as Cal. NH36A for use by other watch makers. It is closely related to the date-only Cal. 4R35.
Cal. 4R36 was introduced around 2010 and used in the Prospex Automatic watches, Model SRP581 and SRP583 around 2014. 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.
Note that Cal. NH36A is rated at -20/+40 seconds accuracy while Cal. 4R36A is rated at -35/+45 seconds. Seiko produces Cal. NH36 in a variety of color and date window variations with black text on a white dial and day and date wheels or reversed, and with the day and date at 3:00 or 6:00. Day wheels are available in English/Spanish, English/Arabic, or English/Chinese.
Hand winding is accomplished with the crown in first position, rotating clockwise. Quick date correction is accomplished with the crown pulled out in second position, rotating counter-clockwise. Rotating the crown clockwise in second position corrects the day wheel.
|Spron 510 Mainspring|
NH71A (skeleton, gilt)
|Day and Date||4R36A|
|Date, 24 Hour Subdial||4R37A|
|24 Hour Subdial||4R39A|
|Date by Pointer|