Quick answer
Most fake Lange 1 Moon Phase watches copy the dial layout well and the moon phase badly. The real display runs off a gear train that moves the moon about 12 degrees each day, so one full lunar cycle takes 29 days, 12 hours and 44 minutes. Many replicas print a moon on a 24 hour disc, or fit a disc that never turns. Judge a copy on three points: case size, moon phase cycle, and the finish of the movement behind the caseback.
What the genuine reference does
The Lange 1 Moon Phase is a hand wound watch in a 38.5 mm case, built on the asymmetric Lange 1 grid. Hours and minutes sit in an off center main dial at 9 o'clock, small seconds at 5, the outsize date at 1, and the power reserve at 3. The moon aperture carries a gold moon and stars on a dark blue disc. Lange states the display drifts by one day every 122.6 years. Current versions pair the moon phase with a day/night indication, a detail most copies skip or fake with printed color.
What to have on hand
- A 10x loupe
- Digital calipers
- A phone with a timer and calendar
- A catalog photo of the reference dial
How to check a replica Lange 1 Moon Phase
- Measure the case across the bezel with calipers. A correct copy reads 38.5 mm. Anything at 40 mm or above is a different case.
- Measure the thickness at the center of the caseback. The genuine is about 10 mm. Copies often run 11.5 to 13 mm because the movement is thicker.
- Set the watch to a known time and photograph the moon aperture with the loupe braced against the case.
- Wait 24 hours and shoot the aperture again from the same angle. The moon should shift about 12 degrees, near one thirtieth of the visible path. A jump to a new phase means a 24 hour disc.
- Repeat the photo check over three days. A true moon phase creeps forward in small steps. A fake sits still or snaps.
- Watch the outsize date at midnight. Both discs must move at the same moment. If only the units disc turns, the tens disc is printed or fixed.
- Press the recessed date corrector. The date should advance one day per press with a clean click.
- Pull the crown to the time setting position and watch the moon disc. Some copies link the moon to the hour hand, which is wrong.
- Wind the watch full and check the power reserve hand. It should climb toward the top of the scale across about 72 hours and fall as the mainspring unwinds. A dead hand is common on cheap copies.
- Turn the watch over. The genuine movement shows a three quarter plate with Glashutte ribbing, screwed gold chatons, blued screws, and a balance cock with hand engraving. Any automatic rotor is a clear sign of a fake, since the reference is hand wound only.
- Weigh the watch in your hand. Gold cases feel dense for the size. Plated brass and steel copies feel light.
- Read the dial print under the loupe. The minute track, the signature, and the Made in Germany text should have sharp edges and even spacing. Fuzzy or crowded letters point to a copy dial.
Where replicas fail
- Moon phase run by a day disc instead of a 29.5 day gear train
- Case 1.5 to 3 mm wider than the reference
- Outsize date built from one disc with printed numerals
- Automatic movement in a watch that should be hand wound
- Power reserve hand that does not track the mainspring
- Flat printed moon with wrong depth, star count, or blue tone
Before you buy
Ask the seller for a video of the moon phase moving over two days and a clear photo of the movement. A seller who cannot supply either has not checked the watch. Keep in mind that a replica stays a replica at resale, service, and repair, and that passing one off as genuine is fraud in most countries.