4S15 is one of a family of high-end automatic watch movements from Seiko. Other closely-related members of this 4S family include the 4S12, 4S24, 4S25, 4S27, 4S28, 4S35, 4S36, 4S71, 4S76, 4S77, and 4S79.
The 4S family was introduced in 1992 with the 4S35 as a higher-end automatic alternative to the mainstream 700x and 7S families. The line is based on the King Seiko 5200 series from the 1970's. Unlike most other Seiko movements, the 4S family operates at 28,800 vph and includes both automatic and hand winding variants.
The 4S15 was a high-end movement, adjusted to +15/-10 seconds per day from the factory. This is nearly as accurate as the "Top" grade ETA 2892 and similar movements. It features a thermo-compensating balance and hairspring, and the movement hacks and can be wound by hand. Cal. 4S15 was only used in two watches: The Seiko SCVK001 and SCVK002, both targeted at the European market. A nearly-identical movement, Cal. 4S71, was used in Credor watches and is gold plated. A less-adjusted movement, the 4S15, appeared later and is the most common of the family.
Once Seiko introduced the 6R family, the 4S was moved upmarket and the simple movements were discontinued. The series was refreshed in 1995 with the addition of the more-complicated 4S71 and derivatives. These remove the date window and add subdials and complications such as small seconds, retrograde day, date and 24 hour subdials, and power reserve indicators. Since 2007, the 4S series has been limited to Seiko's Credor range.
This family of movements powered Seiko's line of GMT and dual timezone watches, inheriting that task from the 6200 and 6100 series of the 1960's and the 5600 series of the 1970's and lasting from the mid-1990's through 2013.
The Calibre 4S family is assembled at Seiko's Shizukuishi Watch Studio in Morioka, Iwate prefecture, Japan, along with other high-end Seiko movements.
The 4S family operates at 28,800 A/h, an unusually high beat rate for Seiko.
There are essentially three "generations" of 4S movements:
- The 4S15 and derivatives (4S12, 4S15, 4S24, 4S25, 4S28, and 4S35) are simpler movements with few complications directly derived from the 5200 line. They were used for mid-range watches while Seiko developed the less-expensive 6R family of movements.
- The family moved upmarket with the 4S71 and derivatives (4S77, 4S79, and 4S79A). These add complications to compete with higher-end Swiss watches and powered the first Brightz and Credor automatics. The ultimate 4S movement was the hand-crafted 4S79 used in the limited-edition Credor GBAY992 and GZAY999 (limited to 500 and 20, respectively), with a weight attached on the hairspring like the King Seiko 44KS for chronometer accuracy.
- The final family members were complicated movements exclusively used in Brightz and Credor watches, including the 4S27/4S77 and 4S36/4S76.
Special note: The 4S15, 4S25, and 4S35 are all essentially the same movement. The 4S15 is the base model, with the 4S25 being essentially identical on paper. The 4S35 is adjusted to +15/-10 seconds per day, while the others are certified to +25/-10.
|4S12||1997-1998||Automatic||Hours, minutes, seconds, 24 hour GMT||Date||None||25|
|4S35, 4S25, 4S15||1992-1997, 2000||Hours, minutes, seconds|
|4S24||Manual||Hours, minutes, seconds||None||21|
|4S28||Hours, minutes||Small seconds||24|
|4S71||1995||Automatic||Hours, minutes, seconds||None||None||25||40 Hours|
|4S77, 4S27||1996-2006||Subdial||Date, retrograde day, 24 hour GMT||28||50 Hours|
|4S76, 4S36||2004-2013||Date, retrograde day, 24 hour GMT, power reserve indicator||31|
|4S79, 4S29||Hours, minutes||None||Small seconds, power reserve indicator||40 Hours|
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