Quick answer
A fake Patek Philippe ref. 3940 is a replica built to copy the look of Patek Philippe's 1985 perpetual calendar, not its mechanics. The genuine watch runs on calibre 240 Q, a micro-rotor automatic with a true perpetual calendar module that tracks day, date, month, leap year, moonphase and a 24-hour indicator without correction until 2100. Replicas run stock automatic or quartz movements under a decorated rotor, so those same displays are cosmetic or driven by a simple annual-style calendar. Judge a replica on dial layout, subdial placement, case size, thickness and finishing. It remains a replica and must never be sold or represented as a genuine Patek Philippe.
Prerequisites
- Daylight photos of the actual watch, not manufacturer or catalog images
- A caliper, or a ruler and steady hand, for the case diameter and thickness
- Familiarity with the real layout: day and 24-hour at 9 o'clock, month and leap year at 3, date and moonphase at 6
What the reference 3940 actually is
Patek Philippe launched the ref. 3940 in 1985 and kept it in the catalog until roughly 2007. The case measures about 36 mm across and about 9 mm thick, which is slim for a perpetual calendar because the 240 Q micro-rotor sits flush with the base plate instead of stacking on top of it. The dial carries three subdials plus a small leap-year aperture and a 24-hour track, all printed in a tight, even typeface. Cases were produced in yellow gold, rose gold, white gold and platinum. That combination of small size, thin profile and complex calendar is what replicas struggle with most.
What replica 3940s are in practice
- Cases that measure 39 mm to 42 mm, because the donor movement will not fit a 36 mm shell
- Thickness of 11 mm to 13 mm against the genuine 9 mm
- Gold plating over steel or brass, or plain stainless steel sold as gold
- A full-size rotor or an engraved plate hiding a quartz module
- Printed moonphase discs that jump instead of sweeping
- Subdials that move together or that no longer match the pusher functions
How to check a replica 3940 step by step
- Measure the case diameter and note the number. Anything above 38 mm is not a faithful copy of the reference.
- Measure the thickness at the crystal edge and at the caseback. Anything over 10 mm signals a donor movement with a bolt-on calendar.
- Confirm the subdials sit at 3, 6 and 9 o'clock and that the day and month windows show the correct wording and font weight.
- Set the watch to February 28 and advance it. A genuine perpetual calendar rolls to February 29 and then to March 1 with no correction. A replica skips, sticks or requires the pusher to be pressed twice.
- Track the moonphase over several nights. The genuine disc creeps forward. A printed replica disc snaps in one jump.
- Turn the watch over and look for the micro-rotor. On a genuine 240 Q the rotor is a small half-moon inset into the movement. A full disc rotor fills the caseback and is the clearest single tell.
- Inspect the case flanks with a loupe. Genuine bevels are crisp and hand-finished where the bezel meets the midcase. Replicas show rounded edges and tool marks.
- Weigh the watch. An 18k gold 3940 is noticeably heavy for its size. Plated replicas feel light and hollow.
- Check the crown and the recessed correctors on the caseband. Genuine correctors are set flush and need a pin tool. Replica correctors often stand proud and press easily with a fingernail.
Dial and printing checks
Compare letter spacing in the brand name and the city line against reference photos. Replica dials usually set the text too wide, thicken the strokes, or place the signature too high. Look at the printed minute track and the small leap-year digits. On replicas these are often smudged or unevenly spaced because they come from a scan rather than a retouched die.
Movement checks
Ask for a video of the balance wheel in motion. A micro-rotor automatic has a slow, smooth beat and the rotor swings in a tight arc. A quartz replica shows a ticking seconds hand if one is present, and the rotor, if fitted at all, spins freely with no winding resistance. No replica on the market reproduces the 240 Q architecture, so any claim of a clone movement is marketing.
Case and hallmark checks
Genuine gold cases carry crisp hallmarks on the caseback and the lugs. Replicas stamp them shallow or omit them. Check the lug profile as well. The 3940 has short, downward-curving lugs that hug a small wrist, and replicas often straighten them to fit larger cases.
Price expectations
Replica 3940s sell from roughly 80 US dollars for a quartz version to around 400 dollars for the better automatic builds. Genuine examples in gold trade at auction in the five-figure range and above. Any 3940 offered for a few hundred dollars is a replica, and any seller claiming otherwise is misrepresenting the watch.
Legal and honesty rules
Replica watches infringe trademarks and can be seized by customs in the United States and most other countries. Buy and wear one as a replica, disclose it as a replica if you ever resell it, and never present it for service, insurance or appraisal as a genuine Patek Philippe. Passing a counterfeit as real is fraud, and that risk sits with the seller, not the watch.