Quick Answer
A fake Patek Philippe perpetual calendar moon phase is judged on three points: moon phase gearing, calendar advance, and case dimensions. A genuine Patek Philippe perpetual calendar moon phase display stays accurate to one day in 122 years. Most replicas run a simplified 29.5 day disc that slips about a day every three years. Set the watch, track it, measure it. A replica fails at least one of those tests.
Prerequisites
- The exact reference number you are checking, such as 5320G or 5740/1G.
- Published specs for that reference: diameter, thickness, lug to lug, lug width, weight.
- A 10x loupe and a phone with a macro lens.
- Digital calipers and a small kitchen scale.
- A lunar almanac or a moon phase app.
- A plastic pusher tool for the case correctors.
Step-by-Step Check
- Write down the reference number and its factory specs before you handle the watch. Subdial layouts differ between references, so a correct layout on one model is a defect on another.
- Measure the case across 12 to 6, across 3 to 9, and lug tip to lug tip. Compare each number to the published figures. A case that runs 0.4 mm thick or 1 mm wide shows on the wrist.
- Weigh the watch on the scale. A steel perpetual calendar on a bracelet should land within a few grams of the listed weight. A light case points to a different alloy.
- Set the watch to a date you can verify, then wind the crown forward past midnight. On a genuine perpetual calendar the day, date, month, and moon phase all snap near midnight. Many replicas move them at 3 a.m. or need the correctors pushed by hand.
- Examine the moon phase aperture with the loupe. The two moons should show photographic crater detail and clean edges. Painted dots and blurry prints are common on fakes.
- Photograph the dial straight on and overlay the image on a genuine dial photo at the same scale. Check subdial spacing, aperture size, and the position of the printed minute track.
- Track the moon phase for two weeks against an almanac. A genuine disc lands within hours of the true lunar position. A simplified replica drifts within days at the aperture edge.
- Push each case corrector with the plastic tool. The pushers should have a short, crisp travel. Long or mushy travel points to a copied case with generic springs.
- Ask for a macro photo of the movement through the caseback. Look for Geneva stripes, rounded bevels, and blued screws. Patek Philippe finishes movements by hand, so a stamped plate or laser etching stands out.
- Inspect the caseback engraving and hallmarks under the loupe. Check for sharp edges and consistent depth across the letters.
Where Replicas Fail Most
The calendar mechanism is the first failure point. A true perpetual calendar handles leap years on its own. A replica with a modular calendar needs manual correction in February and again in non-leap years, so ask the seller to walk the watch from February 28 to March 1 on video. The moon phase disc is the second failure point. Cheap discs use one printed pattern repeated twice, so the two moons look identical and sit at the wrong angle. Genuine discs show two distinct moons with correct crater shading.
Movement finishing is the third failure point. Replicas built on a stock automatic movement often hide the rotor or use a decorated plate. Ask for a clear photo of the balance area, the jewel settings, and the bridge edges. Hand-finished anglage catches light in a way that a machined edge does not.
Legal Note
Importing a counterfeit watch into the United States is illegal and the goods can be seized. Selling a replica as a genuine Patek Philippe is fraud. Keep any replica listed as a replica, and never pass one to a buyer as original.