44 mm case. 21 mm lug width. A bold, statement-size wear. Best suited to larger wrists where the case sits flush.
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A Sedna gold chronograph, and the single most useful thing to know is that this reference IS a chronograph. It is routinely listed as a plain Seamaster Diver 300M, which is a different and much cheaper watch.
Known issues in the market
Omega's own model name for this reference is "Seamaster Diver 300M Co-Axial Master Chronometer Chronograph 44 mm". A listing describing a three-hand diver at this reference has the wrong watch or the wrong number.
Sedna gold is Omega's own red-gold alloy and is not the same as a plated case. Wear through to a different colour underneath is decisive.
The dial is black ceramic with the waves in positive relief, and the subdial rings and hands are Sedna gold rather than plated brass.
Area
What to check
What is correct
Red flag
dial
Chronograph registers present
Two subdial registers plus small seconds, with Sedna gold rings
A three-hand dial, which is a different reference entirely
dial
Laser-engraved waves in relief
Waves standing proud of a polished ceramic surface, catching light separately
A printed wave pattern flush with the dial
movement
Cal. 9901 and Master Chronometer papers
Column-wheel chronograph with a 60-hour reserve; METAS certificate matching the watch
A missing certificate on a watch sold as full-set, or a reserve well short of 60 hours
case
Sedna gold colour continuity
Even alloy colour at wear points, lugs and bracelet interfaces
Any colour change at an edge, which indicates plating
Common legitimate replacements
Rubber straps are consumable and replaced routinely.
Ceramic bezel inserts are replaced after damage; ceramic chips rather than scratches.
Expert resources: An Omega boutique can confirm the reference and re-issue Master Chronometer data. The steel Diver 300M entries in this catalog cover the shared case and crown tells.
