Seiko 4S12

	Brand:	Seiko
	Family:	Seiko 4S Family
	Height:
	Jewels:	25
	Reserve:	40 hours
	Frequency:	28,800 A/h
	Winding:	Automatic, Bi-Directional Automatic Winding
	Diameter:
	Complications:	24 Hour Hand, Date, GMT Hand, Hacking Seconds, Hand Winding, Quick Date Correction
	Hands:	Central Hour Hand, Central Minute Hand, Central Seconds Hand, Date Window at 3:00

Distinguishing Technical Characteristics
Clockwise Balance Cock Screw Regulator Balance Balance at 4:30 Barrel at 12:00
Production: 1997 – 1998
1910s	1920s	1930s	1940s	1950s	1960s	1970s	1980s	1990s	2000s	2010s	2020s

Cal. 4S12 is an automatic movement with date and 24 hour hand developed by Seiko in the early 1990s. It was based on the Seiko 52 stream of movements, which had been retired in 1976, and was responsible for Seiko’s resurgence as a maker of high-end watches. Cal. 4S12 is very similar to Cal. 4S15, which lacks the 24 hour hand.

The 24 hour hand is located centrally on the dial, coaxial with the ordinary timekeeping hands. It is not adjustable separately from the 12 hour hand. This leads some to consider it not to be a “true GMT”, though this is the same function as the famous Rolex GMT-Master.

Cal. 4S12 was used in the SUS GMT military watch, which included an internal rotating bezel to enable the user to “set” the GMT hand for a second time zone.

• Seiko SUS SCFF005
• Seiko SUS SCFF007
• Seiko SUS SCFF009

Early Seiko 4S Movements

From the 1992 introduction of the Seiko 4S family through the early 2000s, Seiko used the 4S line as a high-end movement for diverse watches, including the SUS military, Alpinist, and Titanium diver. Most of these models were retired shortly after introduction, and the series of simple 4S movements was phased out by 2003.