Short answer
Hippocampus is Omega's seahorse emblem. Co-Axial Master Chronometer is a movement certification from METAS, the Swiss Federal Institute of Metrology. A replica with these markings copies the caseback engraving and the rotor text. It does not carry a METAS certificate card. It does not pass the 15,000 gauss magnetic test. Buyers get the look of a Seamaster Aqua Terra, Diver 300M, or Planet Ocean, not the certification.
What the hippocampus mark is
Omega registered the seahorse as a logo in 1957. Genuine Seamaster casebacks carry the emblem as a stamped relief. The shape has a curved tail and a trident. On replicas the mark appears two ways: etched into the caseback steel, or printed on the rotor. Etching depth is the quick test. A shallow, flat mark with soft edges points to a lower tier build. Deep relief with clean borders matches high-tier replica cases.
What Co-Axial Master Chronometer covers
- Co-Axial: an escapement design Omega put into series production in 1999 with caliber 2500. Fewer sliding contacts at the pallet stones than a lever escapement.
- Master Chronometer: METAS certification that started in 2015. Eight tests over 10 days on the finished watch, not the bare movement.
- Magnetic resistance: 15,000 gauss. Genuine parts include a silicon balance spring and non-ferrous components.
- Rate: 0 to +5 seconds per day across the test set, measured in six positions and at two temperatures.
- Paperwork: a METAS certificate card with a number that ties to the watch.
What a replica delivers
High-tier replicas ship with an automatic movement, a sapphire crystal, a screw-down crown, and a display caseback. Common movements are the Asian 2824 clone, the Miyota 9015, and decorated copies with Omega-style rotor text. Beat rate is 28,800 vph on most of them. Rate accuracy sits in the -10 to +20 seconds per day band. Real numbers need a timegrapher reading from the seller.
Three things do not transfer: the METAS certificate number, the 15,000 gauss rating, and the silicon balance spring. Replicas also run thicker. Plan on 0.3 mm to 0.8 mm more case height than the genuine reference.
Reference points to compare
- Aqua Terra 41 mm: 20 mm lugs, 150 m water resistance on the genuine.
- Seamaster Diver 300M 42 mm: 20 mm lugs, helium escape valve at 10 o'clock, ceramic dial.
- Planet Ocean 39.5 mm and 43.5 mm: 21 mm lugs, 600 m water resistance on the genuine.
Checks before you buy
- Caseback relief depth and border sharpness.
- Rotor engraving: fill color, font weight, spacing.
- Crown thread count and bezel click feel.
- Movement photos and a timegrapher screenshot.
- Lume color under a UV light: blue on Diver 300M, green on some Aqua Terra dials.
Prices
High-tier replicas run about $250 to $600. Genuine Seamaster models start near $6,000 for steel on a strap and go past $9,000 for precious metal. A service on a genuine Master Chronometer movement at an Omega service center costs about $500 and up. A replica movement is swapped, not serviced.
Unknowns
Factory names change. Movement batches change. A seller's stock photos may show a different build than the unit shipped. Ask for photos of the actual watch.