Seiko 4R38

	Brand:	Seiko, Seiko Instruments Inc.
	Family:	Seiko 4R Family
	Height:	5.32 mm
	Jewels:	24
	Reserve:	40, 41 hours
	Frequency:	21600 A/h
	Winding:	Automatic, Bi-Directional Automatic Winding, Central Rotor 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

Distinguishing Technical Characteristics
Central-Rotor Automatic Counter-Clockwise Balance Cock Etachron Regulator Balance, Balance at 3:00
Production: 2012 – Current
1910s	1920s	1930s	1940s	1950s	1960s	1970s	1980s	1990s	2000s	2010s	2020s

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.

Cal. 4R38A is also used in the Seiko Original line, where the company specifies accuracy to -35/+45 seconds per day and 41 hours power reserve.

Seiko 4R38 Operation

The movement can be manually wound with the crown in position 1. Rotate the crown clockwise to wind the mainspring.

The time is set with the crown in second 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.

There are only a few complicated members of the family, with a 24 hour subdial (4R37 and 4R39), or date by pointer subdial and power reserve indicator (4R57).

External Link

Manufacturer Link