Model: Credor “COSC” GBAY992 / 4S79-0050 Chronometer
Year: February 1998
Limited Edition: 500 Pieces
Features:
The Origin. In 1997, Seiko crossed enemy lines and sent hundreds of movements to COSC in Switzerland for chronometer certification. Each movement was adjusted and regulated by one man - Akira Ohira. Over the years, his deft touch had earned him the nickname "God’s Hands", so you know he wasn’t about to let Seiko down. The result? 520 movements came back to Japan as certified chronometers.
The Certification. The reason for COSC’s existence is a long story. In summary, Switzerland ran the Observatory Trials for over a century, until Seiko disrupted the status quo by sweeping the competition with its 4520 calibre and newly invented quartz movements. Switzerland wasn’t pleased, and the Observatory Trials were shut down. A strikingly similar standard, called COSC, would emerge a few years later in 1973, but it had one crucial difference - all movements now had to be Swiss.
The Oddity. Why would COSC certify a Japanese-made calibre, especially from the very company that had rattled Switzerland’s dominance during the original trials? This should be such an answerable question - and trust me I’ve tried. I’ve contacted Seiko, Credor, the Ginza museum, journalists, veteran dealers in Japan, and even COSC themselves. Yet no one has been able to explain why COSC accepted 520 calibres made in Japan.
The One-off. Despite the unanswered questions, one fact remains: in 1997, Seiko would release its first and only official COSC chronometers. But why didn’t Seiko continue the practice? Because in 1998, the Grand Seiko Standard was born, and its technical (not geographical) requirements were even stricter than COSC.
The Design. And just like the movement, the watch itself carries a subtle Swiss connection. The guilloché-style dial pairs elegantly with a milgrain bezel - and the whole thing is solid 18k gold, giving the watch a distinctly dressy character. Through the exhibition caseback, the calibre is technically visible but its inner workings are mostly hidden behind a full plate. When you’re sending a movement to COSC, choosing function over form is only logical - so we can hardly fault Seiko for prioritising stability over decoration.
The Papers. Collectors in Japan are famously casual about keeping documentation, often for privacy reasons, but it’s still surprising how rarely full sets appear for a watch whose papers are so historically significant. So if you do pick up this piece - today or in the future from someone else - please take care of the box and papers, because there won’t be another Japanese-made Swiss-certified chronometer.
Specifications:
Condition: In great condition overall. Swirls and hairlines can be seen on the solid gold case, but there are no marks of any significance.
Scope: Full box and papers, including the original COSC certificate. The inner box is showing signs of aging.
Movement: 4S79 Manual-wind, with power reserve and small seconds. Certified by COSC in Switzerland.
Dimensions:
- Case Width: 35.2mm
- Lug to Lug: 39.0mm
- Case Thickness: 8.3mm
- Lug Width: 18mm
