6S78 is one of a family of column wheel chronograph movements from Seiko. Other closely-related members of this 6S family include the 6S74, 6S77, 6S99, and 6S37

The 6S family was introduced in 1998 to power Seiko's 3-register Credor “Phoenix” chronographs. The project was a major development for Seiko, with the company calling in watchmakers from retirement to develop a truly modern and advanced movement. The resulting 6S78 was critical in showing that Seiko could compete in the resurgent high-end mechanical watch market. The “Phoenix” chronograph series were marketed exclusively in Japan and were embraced for this reason.

The first calibre was the automatic 34 jewel 6S78, and this is the basis for this family. The 6S78 was used for the Credor Phoenix Chronograph, model GCBP, from 1999 through 2004.

In 2001, Seiko also released a special high-end Prospex Flightmaster, model SBDS001, with Cal. 6S37 which added a power reserve indicator at 2 30 on the dial. This remained in production through 2011. Cal. 6S37 was also used in the Brightz Phoenix Chronograph, model SAGH, and Credor Signo chronograph, model GCBK, from 2010 through 2016. The Credor version of this movement was Cal. 6S77, which was used in the Credor Pacifique chronograph, model GCBK, from 2003 through 2005.

The high-end Credor mechanical chronograph, model GBBL993, was introduced in 2002 and produced through 2005. It used Cal. 6S99, a gold-plated skeletonized version. The hand winding 35 jewel 6S74 variant adds a power reserve indicator, and is identical to the skeletonized 6S99.

In 2005, Seiko introduced Cal. 6S28, which was essentially similar to the original 6S78. It was used in the Brightz chronograph, model SAGP, through 2007 before moving to the Brightz Phoenix chronograph, model SAGH, from 2008 through 2013. In 2012, Cal. 6S28 was redeployed for the Ananta brand in the limited-edition Automatic Chronograph, model SSD001, and SAEH line. These were out of production in just a few years.

A final variant is the automatic 6S96 which is similar to the 6S77 but lacks the date window and 2 jewels but thus gains an additional 10 hours of power reserve.

The Calibre 6S family is assembled at Seiko's Shizukuishi Watch Studio in Morioka, Iwate prefecture, Japan, along with other high-end Seiko movements. Although the lower initial number (6) might indicate otherwise, the 6S chronograph is generally considered a higher-end movement than the 8R family. This despite the fact that the newer 8R has a vertical clutch rather than the oscillating pinion of the 6S.

The TAG Heuer Calibre 1887 is a derivative of the Seiko 6S37.

• 6S28
  • Ananta (SAEH, SSD), Brightz Phoenix (SAGH)
• 6S37
  • Credor Signo (GCBK), Prospex Flightmaster (SBDS), Brightz Phoenix (SAGH)
• 6S77
  • Credor Signo and Pacifique (GCBK)
• 6S77
  • Credor Phoenix (GCBP)
• 6S99
  • Credor (GBBL)

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• Seiko 6S28, 6S37 Manual
• Seiko Credor 6S37, 6S74, 6S77, 6S78, 6S96, 6S99 Manual
• Seiko 6S Family Reference