Quick answer

A fake Audemars Piguet Royal Oak Perpetual Calendar gives itself away through the calendar, not the dial printing. Reference 26574 runs the in-house caliber 5134 and measures about 9.5 mm thick. Most replicas hide a modified third-party automatic movement behind a decorative plate, add 2 to 4 mm of case thickness, and cannot track a leap year or the week-of-year ring. Test the calendar function first. If the watch cannot roll from February 28 to March 1 on its own in a non-leap year, nothing else on the watch matters.

What you need before you start

  • Digital calipers that read to 0.01 mm
  • A 10x loupe or a macro lens on a phone
  • Reference photos of the exact reference number you are inspecting
  • The seller's case number, service history, and asking price
  • A bright, even light source and a soft cloth

Inspection steps

  1. Measure the case thickness at the center of the caseback with the calipers. A reading above 11 mm on a 26574 is a fake.
  2. Weigh the watch with the bracelet at full length. A steel 26574 sits near 150 grams; a plated alloy case feels light for its size.
  3. Read the outer week ring with the loupe. Numerals should be sharp and evenly spaced across all 52 positions, with the week hand pointing cleanly at the current number.
  4. Push each recessed corrector on the case flank with the setting tool and confirm that day, date, month, and moonphase each advance on their own.
  5. Set the watch to a known date and let it run through February 28 of a non-leap year. A true perpetual calendar jumps to March 1 with no correction.
  6. Examine the moonphase disc under magnification. Genuine discs are metallic with a grained surface; replicas use flat printed discs with visible banding.
  7. Tilt the dial under the light and study the Grande Tapisserie grid. Genuine squares are raised with sharp edges; copy dials look shallow and softened.
  8. Check the eight bezel screws. They should sit flush, show a polished slot, and line up in one consistent direction.
  9. Read the caseback engraving. Reference number, case number, and metal hallmarks are cut deep with even letterforms on a genuine piece.
  10. Look through the sapphire caseback at the movement. Caliber 5134 shows Geneva stripes on the bridges, beveled edges, and a skeletonized gold rotor carrying the AP crest.
  11. Request an Extract from the Archives from the brand using the case number. A genuine case number returns a matching record; a counterfeit returns nothing.

Bracelet and clasp checks

  1. Run a fingertip along the bracelet flanks. Genuine links have beveled and polished edges with a sharp break between brushed and polished surfaces.
  2. Open the clasp and inspect the engraved logo. The engraving is cut deep, not laser-etched at the surface.
  3. Check the link screws. Heads should sit flush with clean slots; on fakes the heads strip or sit proud of the link.

Papers, serials, and service

Authorized service centers verify the case number before accepting a watch, so a counterfeit cannot be serviced, repaired, or registered by the brand. Treat a missing case number, a mismatched reference on the paperwork, or a seller who refuses a service-center inspection as a fatal flaw. Counterfeit watches also face seizure at U.S. import under trademark law, which means a buyer has no lawful route to resell or ship one.

Red flags that end the inspection

  • The calendar needs manual correction at the end of February.
  • The case measures 12 mm or more.
  • Week numerals crowd or overlap near 51 and 52.
  • Bezel screws sit above the surface or point in random directions.
  • The seller refuses to let you test the calendar function or have the watch verified.
  • The price sits far below market for the reference and the seller pushes for a wire transfer.