|Brand:||Seiko, Seiko Instruments Inc.|
|Reserve:||40, 41 hours|
|Winding:||Automatic, Bi-Directional Automatic Winding, Central Rotor Automatic Winding|
|Diameter:||27.40 mm (12 ligne)|
|Complications:||Bilingual Day Wheel, 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|
Counter-Clockwise Balance Cock
|Production: 2010 – Current|
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.
Seiko 4R36 Operation
The movement can be manually wound with the crown in position 1. Rotate the crown clockwise to wind the mainspring.
The day and date wheels are advanced with the crown in second position (one notch out). Turn the crown counter-clockwise to advance the date wheel by one day. Turn the crown clockwise to advance the day wheel.
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.
Seiko 4R Family Overview
Introduced in 2008, the Seiko Instruments Inc. (SII) 4R family is a mainstream automatic watch movement used in many Seiko models and offered to third parties by Time Module Inc. (TMI). It is an evolution of the Seiko 7S family of movements, produced since 1996, and is related to the higher-end Seiko 6R family.
All movements in the 4R family operate at 21,600 A/h and measure 12 ligne (27.4 mm) in diameter by 5.32 mm in height. Cal. 4R15 and 4R16 have 22 jewels, Cal. 4R35A has 23 jewels, and all other 4R and NH movements have 24 jewels. The NH series movements sold by Time Module Inc. (TMI) are rated as slightly more accurate from the factory, at -20/+40 rather than -35/+45 for the Seiko branded movements, and some differ in the finish, number of jewels, and rated power reserve.
Seiko 4R Movements
There are two branches of the family: The 4R1x movements (4R15, 4R16) came first and have an advanced Spron 510 mainspring but lack hacking and hand-winding. The 4R3x movements (4R35, 4R36, 4R37, 4R38, 4R39, 4R57, 4R71) appeared after 2010 and have a traditional mainspring but add hacking and hand-winding. The 6R family has both improvements.
|Spron 510 Mainspring|
NH71A (skeleton, gilt)
|Day and Date||4R36A|
|Date, 24 Hour Subdial||4R37A|
|24 Hour Subdial||4R39A|
|Date by Pointer|