OMEGA · Seamaster Planet Ocean 600M and Seamaster 300

OMEGA 217.30.42.21.01.001 vs OMEGA 234.30.41.21.03.002

9 published specifications differ between these two, and 5 are identical. Every figure below is what the manufacturer states for that reference; nothing is inferred from the other watch.

What differs

Specification	OMEGA Planet Ocean 600M Co-Axial Master Chronometer 42mm, black dial217.30.42.21.01.001	OMEGA Seamaster 300 Co-Axial Master Chronometer 41mm, blue dial234.30.41.21.03.002
Case	Steel, 42 mm	Steel, 41 mm
Diameter	42 mm	41 mm
Thickness	13.79 mm	13.85 mm
Lug to lug	47.5 mm	48 mm
Water resistance	60 bar (600 metres / 2000 feet)	30 bar (300 metres / 1000 feet)
Crystal	Flat scratch-resistant sapphire crystal with anti-reflective treatment on both sides	Domed, scratch-resistant sapphire crystal with anti-reflective treatment inside
Dial	Black	Blue
Clasp	Foldover clasp with comfort setting and diver extension	Foldover clasp with comfort setting
Movement notes	Listed by OMEGA as a Master Chronometer certified watch. Total product weight approximately 177 g.	Listed by OMEGA as a Master Chronometer certified watch. Total product weight approximately 156 g.

What is identical

Worth knowing as much as the differences: these are the specifications you cannot use to tell the two apart.

Lug width: 21 mm
Bracelet: Steel
Calibre: Omega 8912
Movement: Self winding
Power reserve: 60 hours

What the differences cost you

Each note below follows from the published figures in the tables above — what they mean for intake, for a listing, and for the handover. Nothing here estimates a price or a margin.

Do not describe these the same way

600 metres on the 217.30.42.21.01.001 against 300 on the 234.30.41.21.03.002. Both are more than daily life asks for, so the number is a listing-accuracy question rather than a practical one: quote each watch its own figure, and remember that neither rating survives an unserviced case by itself.

What to check on each

217.30.42.21.01.001

Unfold the diver extension completely and check the hinge is not sprung and that it lies flat again when closed. On a watch that has never been dived it has been shut since new.
Examine the flat crystal's outer anti-reflective coating for wear. OMEGA treats both faces on this reference, so unlike the inside-only crystals elsewhere in the range there is a coating here you can actually scratch.
Do not quote the 600-metre rating as a present-day measurement on a used example. It describes the case as built, and nothing about an unserviced watch confirms it.

234.30.41.21.03.002

Confirm the calibre is the 8912 before quoting anything else. This carries a different movement from the Diver 300M despite the identical depth rating, and their published reserves differ.
Check the lug width against the published 21 mm. That is an odd size that almost no aftermarket strap maker stocks, and a buyer planning a strap change should hear it from you.
Measure the fit using the published 48 mm lug to lug rather than the 41 mm diameter, which understates how this case sits.

Sources

Not affiliated with OMEGA. Specifications are read from each manufacturer's own published documentation on the dates shown and may change; the manufacturer's current documentation governs.