A fake Patek Philippe Perpetual Calendar 3940 is a copy of a reference that Patek Philippe produced for roughly two decades, so any example offered without a documented history deserves a close look. The fastest way to separate a counterfeit from a real 3940 is to check three things: the subdial layout, the case profile, and the movement visible through the sapphire back. Copy makers get those three areas wrong more often than any other detail.
What the Patek Philippe 3940 actually is
The 3940 arrived in 1985 and became the reference that defined the modern Patek Philippe perpetual calendar. It is a thin automatic watch, about 36 mm across and around 9 mm thick, offered in yellow gold, white gold, rose gold, and platinum. Inside sits the caliber 240 Q, an ultra-thin automatic movement with a micro-rotor and a calendar module stacked on top.
The dial layout is fixed across the whole run:
- 3 o'clock: month indication with a small leap year aperture below it
- 6 o'clock: date subdial with a moon phase aperture
- 9 o'clock: day of the week subdial with a 24-hour indicator
Dial colors run from silvered opaline to champagne, blue, and black, and later series carry slightly different printing and hands. The 3940 stayed in the catalog into the 2000s, when the 5140 took its place.
Why fakes of this reference are common
The 3940 sits near the top of the Patek range, and that price gap is exactly what attracts counterfeiters. The complication also happens to be easy to imitate on the surface. Three printed subdials and a moon disc cost very little to reproduce, while a true perpetual calendar mechanism does not. Most copies live in that gap: the face looks busy and complicated, but the mechanism underneath is not a perpetual calendar at all.
How to spot a fake Patek Philippe Perpetual Calendar 3940
Subdials and printing
- Copies often borrow the layout from other references, so the month, day, date, and 24-hour indications end up in the wrong positions or in a four-subdial arrangement.
- Genuine Patek printing is fine and crisp, with even spacing and clean accent marks. Fakes tend to show thicker text, uneven letter spacing, and blurred edges under a loupe.
- The moon phase is a common tell. On the real watch it is a proper lunar cycle. Many replicas use a day and night disc that rotates once every 24 hours instead of roughly 29.5 days.
- Subdial hands should be small and leaf shaped, not straight batons.
Case size and profile
- A genuine 3940 is small by modern standards, around 36 mm, and very thin. Replicas frequently measure 38 to 40 mm and sit noticeably taller because the movement plus calendar module takes up more room.
- Lugs are slim and curved. Copies often show chunkier lugs and a softer bezel step.
- Gold cases have a certain heft. A stainless steel case disguised with gold plating feels light in the hand.
The movement through the back
- Caliber 240 Q has a micro-rotor, not a full size rotor. If you can see a rotor that spans the whole movement, it is not a 240 Q.
- Look at the finish: Geneva stripes, chamfered bridges, and an engraved gold micro-rotor. Cheap copies show plain plates and machine marks.
- Look at the correctors used to set the calendar. On copies they are often crude, misplaced, or missing altogether.
Engravings, documents, and provenance
- Caseback engravings on genuine watches are deep, sharp, and correctly spelled. Fakes use shallow laser etching with soft edges.
- Gold hallmarks on the case should match the metal and the era of production.
- Paperwork matters: a certificate of origin, service records, or an Extract from the Archives from Patek Philippe. A watch with no history at this price level is a warning sign, not a bargain.
Replica tiers: what a high-end copy can and cannot do
Replica quality varies widely, and it helps to know the tiers before you judge one.
- Entry level copies use quartz movements, wrong dimensions, and printed dials. They are easy to identify in person.
- Mid tier copies use a basic automatic movement with a calendar module. The dial looks closer, but the case is too thick and the perpetual calendar function is cosmetic.
- High end or super clone copies get closer on case size and dial finish. Even then, the calendar module is usually a modified third party unit, the moon phase is often a 24-hour disc, and the movement finish does not match caliber 240 Q.
No replica of this reference carries a true perpetual calendar that accounts for leap years without correction, and none will be serviced by the manufacturer.
Before you buy or sell a 3940
- Ask for clear photos of the movement, not just the dial.
- Ask for the Extract from the Archives or service paperwork.
- Compare the serial and reference numbers on the caseback and movement.
- Have an independent watchmaker open the case before money changes hands.
- Buy from a dealer or auction house that stands behind authentication.
One legal point worth knowing: selling a copy as a genuine watch is fraud in the United States, and counterfeit goods bearing a protected trademark can be seized at import. If you are buying a replica of the 3940, treat it as a replica and price it that way.
The short version
Judge a 3940 by the subdial layout, the case thickness, and the movement. Real examples are about 36 mm wide, thin, and powered by a micro-rotor caliber 240 Q. Copies usually miss on size, on the moon phase, and on the movement finish. For a replica, expect replica quality. For the real thing, insist on documents and an independent inspection.