Quick answer
A fake Audemars Piguet Royal Oak Offshore 26420 usually fails in four places: case thickness, the Mega Tapisserie dial texture, the flyback chronograph behavior, and the caseback engraving. The genuine watch is a 43 mm Royal Oak Offshore Selfwinding Chronograph with the in-house calibre 4404, a flyback chronograph, a 70-hour power reserve, and a quick-release strap system. A caliper, a 10x loupe, a scale, and ten minutes of hands-on time settle most questions.
What you need
- 10x jeweler's loupe
- Digital caliper
- Scale accurate to 0.1 g
- Stopwatch or phone timer
- Reference photos of a genuine 26420 from a dealer or auction listing
Step by step
- Measure the case with the caliper. A genuine 26420 is 43 mm across and about 14.4 mm thick. Take readings across the 12 to 6 line and the 3 to 9 line. Both should match within a tenth of a millimeter. Fakes typically come in under 43 mm or sit near 15 mm thick.
- Inspect the bezel and case flanks. Genuine surfaces show a clean line where brushed steel meets polished bevels. The eight bezel screws sit flush, with slots of even depth and no burrs or rounded heads.
- Look at the dial with the loupe. The Mega Tapisserie squares should be sharp-edged pyramids with even spacing and consistent depth. Fakes have shallow, rounded, or mismatched squares. Check the AUDEMARS PIGUET printing for crisp edges and no ink bleed.
- Examine the date aperture. Its edges should be cleanly cut and finished, the date centered in the window, and the numeral font consistent with the rest of the dial.
- Test the flyback chronograph. Start the chronograph, let it run, then press the lower pusher once. A true flyback returns to zero and restarts in one motion. Most replicas use a modified chronograph module that stops or resets only after the top pusher is pressed. The pusher should also feel firm, not spongy.
- Watch the chronograph seconds hand. At 28,800 vibrations per hour the hand sweeps in eight small steps per second. A quartz fake jumps once per second.
- Try the interchangeable strap system. The 26420 releases its strap with a tab at each lug, no tools needed. On most fakes the tabs are stiff, misaligned, or absent, and the strap needs a screwdriver.
- Turn the watch over. The display back should show a decorated movement with Geneva stripes, circular graining, and a signed oscillating weight. The caseback rim carries the reference number 26420 and a serial, both engraved, not laser-printed.
- Weigh the watch and compare it to a published figure for the same configuration. Fakes that use plated cases or lighter movements feel off when balanced on a fingertip at the lugs.
- Check the rate on a timegrapher if you have one. The calibre 4404 runs at 4 Hz with a steady amplitude. Erratic readings or a rate that swings more than a few seconds point to a substitute movement.
Tells that show up in photos
Sellers send close crops for a reason. Blown-up shots hide thickness and weight. Ask for a straight-on side profile, a caseback shot at an angle, and a short video of the chronograph starting, running, and resetting. If the flyback does not restart on the first push, stop there. Also compare the crown and pusher proportions. Genuine pushers are tapered and screw down; fakes often look bulky or sit too high off the case.
Where visual checks stop
A well-made fake can pass a photo review and even a loupe pass on the dial. Only a watchmaker who opens the caseback and inspects the movement, the jewel count, the finishing marks, and the engraved calibre number can give a final answer. If a seller refuses an in-person inspection or a third-party authentication, treat that as the answer.