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Omega’s 1952 Seamaster Calendar reference 2627 is identified as the first Omega watch with a date window. Its date sits at 6 o’clock, and its automatic caliber 353 uses a distinctive bumper rotor. The 2627 is a mid-century collectible, not a modern sports watch; a surviving example’s present condition matters more than its original water-resistance rating.
Why the Seamaster Calendar 2627 matters
Omega’s official vintage archive places reference KO 2627 in its 1952 international collection. Specialist coverage and auction catalogues describe it as the first Omega watch with a date window—not the first wristwatch date ever made. The Seamaster line itself began in 1948, according to Christie’s catalogue, which connects its launch with Omega’s centenary.
The 2627’s contribution is easy to see: it brought a calendar display into Omega’s range, integrated into a clean, symmetrical dial rather than treated as a separate subdial. The date appears at 6 o’clock.
How to distinguish early and later date windows
Window shape offers a useful period clue. Christie’s and Fratello describe early examples with square or rectangular date apertures; Christie’s says the design changed to a trapezoidal window from 1953. Fratello also notes variation in dial colors and finishes, including white or cream and black dials, with smooth and waffle textures.
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These are reported variants, not a stand-alone authentication test. A window’s shape should be considered alongside the watch’s case and movement, dial condition, and available provenance.
Caliber 353 and its bumper rotor
Omega’s archive identifies the KO 2627’s movement as an automatic mechanical caliber 353. Fratello’s 2021 account gives further figures: 17 jewels, a reported 42-hour power reserve, and a rate of 19,800 vibrations per hour. Those detailed figures come from the specialist article; Omega’s archive confirms the caliber and movement type.
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The caliber 353 is a bumper automatic. As Christie’s explains, its rotor swings back and forth and meets springs instead of completing a full 360-degree rotation like a modern full-rotor automatic. That different winding action is part of the watch’s mid-century character.
Case, dimensions, and original water-resistance rating
Omega lists the KO 2627 case as gold-cap on stainless steel, with a screw-in case type and an original rating of 3 bar (30 metres / 100 feet). The archive also specifies a leather strap. The rating is a period specification, not evidence that a watch made in the 1950s remains sealed today. Do not expose a surviving 2627 to water unless a qualified watchmaker has assessed and tested that individual watch.
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Dimensions vary across documented examples and descriptions. Fratello’s 2021 article gives approximate reference dimensions of 35.3 mm wide, 42.6 mm lug-to-lug, and almost 12 mm thick. Christie’s records a 34.5 mm case for its circa-1952 14K gold example. Antiquorum’s 2007 catalogue gives 35 mm diameter and 12 mm thickness for a specific stainless-steel CK 2627-3 SC sold in 1953. These measurements describe particular examples or reported dimensions, not a single guaranteed size for every variant.
What to check before buying a vintage 2627
Each surviving watch needs to be assessed on its own merits. Ask for clear photographs and documentation, and have a qualified vintage Omega watchmaker inspect the watch before purchase when possible.
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- Reference and movement: Check the case reference and movement identification, and ask whether the seller can document their consistency.
- Dial and hands: Inspect the dial surface and printing, date window, and hands for condition or replacement. Redials and changed parts can affect originality.
- Case: Confirm the material and look for wear, polishing, or other alterations. Documented examples include gold and stainless-steel cases, so verify the exact variant rather than assuming all 2627s match the KO 2627 archive entry.
- Movement condition and service: Request service records and an inspection or service estimate. A Christie’s catalogue example was described as working when catalogued, but it had not been tested for accuracy and the auction house recommended service; that report applied to that lot only.
- Seller terms: Review the seller’s documentation, authenticity terms, and return policy before committing.
Historical auction records are not a reliable guide to current value. Antiquorum recorded a CHF 2,832 hammer result for its particular CK 2627-3 SC lot in 2007; that is one transaction, not a current price or market average.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Further reading
For a book-length reference, Christie’s cites Marco Richon’s Omega – A Journey through Time, page 277 and plates 2868 and 2758, for examples of the 2627. Availability has not been established here.
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