Short answer
A fake Constellation 131.90 is a replica of an Omega Constellation whose case reference starts with the code 131.90. Omega splits reference numbers into blocks, and 131 marks the modern Constellation case family. The digits that follow describe case size, movement, dial and bracelet. Sellers who quote only 131.90 have dropped the trailing segments, so the string points to a family of watches rather than one model.
What the digits do
Omega reference numbers read in segments. The first block names the collection and case type, which is where 131 sits. The next pair covers diameter and material. Later pairs cover movement, dial and bracelet. A full Omega reference carries five blocks. A listing that stops at 131.90 is a family code, and the watch behind it can differ in size, metal and dial color from the photo you were shown.
Before you start
- A 10x loupe
- Digital calipers
- A kitchen scale that reads grams
- A watchmaker who can open a caseback
Inspection checklist
Work through these checks in order. Stop at the first clear failure.
- Read the reference engraved on the caseback and compare it with the listing text. A genuine Constellation prints every block, not a shortened code.
- Look at the claws on the bezel. The Constellation griffes are four polished claws at 3 and 9 o'clock. Replica versions often sit flat, uneven, or too wide against the crystal.
- Measure the case with calipers and compare the number with the listed diameter. Replica cases run large or small by fractions of a millimeter.
- Weigh the watch head and bracelet. Published specs quote grams, and replicas usually run light because the bracelet links are hollow.
- Check the date window position and the font of the numerals. Misaligned windows and fat type are common faults.
- Ask a watchmaker to open the caseback and photograph the movement. Look for engraved rotor text, jewel count and finish that matches the reference.
- Confirm the Master Chronometer status. Modern Constellation models carry METAS certification, and a replica movement cannot hold that rating.
What replica versions get wrong
- Bracelet end links that do not sit flush against the case
- Crown threads that feel rough or cross-thread on the first turn
- Print on the dial that sits under the crystal instead of on top of it
- Sapphire that shows internal reflections and no anti-reflective coating
- Clasp stamps that use the wrong font weight or depth
Questions to ask before you buy
Ask for the full reference, the case diameter in millimeters, the movement name and caliber number, and clear photos of the caseback and clasp. Ask whether the seller accepts a return if a watchmaker finds the movement is not as described. A seller who cannot answer these four points in writing is describing a generic replica, not a specific 131 reference.