Answer first

Reference 210 is the Omega Seamaster Diver 300M. A fake can pass a photo check. Four checks catch most of them: the laser-engraved wave dial, the beat rate of the movement, the caseback engraving, and the serial numbers. Two of those checks need the caseback off or a timegrapher. Ask the seller for a movement photo and the serial number before money moves.

What the 210 reference covers

Full numbers look like 210.30.42.20.03.001. The 42 marks a 42 mm case. The last block marks the dial: 03 blue, 01 black, 06 grey, 04 white. Water resistance is 300 m. The helium escape valve sits at 10 o'clock. The crown sits at 3 o'clock behind conical guards. The date window sits at 6 o'clock.

Dial and bezel

The dial is polished ceramic. Omega cuts the waves with a laser, so each wave is a groove sunk into the ceramic. Light moves across those grooves when you tilt the watch. Fakes print the pattern or press it into metal, so the waves sit flat or too deep. The bezel insert is ceramic with white enamel in the scale. Real enamel fills the numbers flush. Fake enamel sits above the surface or shows a broken edge. The lume glows blue. Hands are rhodium plated and skeletonized.

Movement

Calibre 8800 runs at 25,200 vibrations per hour. That is 3.5 Hz and 7 beats per second. Power reserve is 55 hours. The escapement is co-axial. The balance spring is silicon. A timegrapher reports the beat rate on screen. A movement at 28,800 vph, which is 4 Hz and 8 beats per second, is not calibre 8800. Many replicas use a 2824 copy at that rate. Newer replicas copy the 3.5 Hz rate, so beat count is one check and not the whole test.

Caseback and serials

The 210 caseback uses the NAIAD LOCK system. Engravings stay upright when the back is tight. The outer edge and the movement both carry a serial number. The two numbers must match, and both must match the Master Chronometer card. A mismatch points to a swapped part or a fake. Case sides are brushed with polished chamfers along the lugs. Fakes show soft or missing chamfers.

Tool checks

• Timegrapher: beat rate, amplitude, rate in seconds per day.
• Caseback off: co-axial escapement, 8800 marking, serial match.
• Lume: blue emission on hands, markers and bezel pip.
• Crystal: anti-reflective coating on both faces, faint blue tint at an angle.

Limits of a photo check

High-grade replicas copy the dial texture and the caseback text. A photo at 1000 px hides the difference. A service center or a watchmaker with a caseback tool gives a firm answer. Budget for that before you buy. Omega lists steel-on-bracelet versions of this model in the mid five-thousand dollar range, and used prices sit lower. A price far under used market for a complete set is a reason to walk away.