Quick Answer
A replica Duomètre moon phase is a copy of the Jaeger-LeCoultre Duomètre à Quantième Lunaire, a watch built around a Dual-Wing movement with two separate gear trains and two power reserves. One reserve drives the timekeeping, the other drives the calendar and moon phase. On a replica, that split architecture is the first thing to verify, because most fakes run a single train and fake the second reserve with a printed dial. The moon phase disc, the jumping seconds hand, and the twin reserve indicators are the three features that separate a serious build from a cosmetic one.
What You Need
- A loupe at 10x for dial printing and disc finish
- A caliper for case and lug measurements
- A timegrapher if you plan to check rate and amplitude
- The reference numbers for the genuine model you are comparing against
- Good light from a low angle to catch dial texture and hand polish
How to Evaluate a Replica Duomètre Moon Phase
- Measure the case across the bezel and confirm the diameter sits near 40.5 mm, then measure thickness at the caseback and compare it to the genuine figure.
- Check the lug width and the curve of the lugs against the reference, since stretched or flattened lugs are a common shortcut on replicas.
- Examine the dial layout: hours and minutes on one side, a small jumping seconds register on the other, twin power reserve indicators, and the moon phase aperture in its correct position.
- Watch the jumping seconds hand for a full minute. It should snap to zero once per second rather than sweep.
- Verify that both power reserve indicators move independently when you wind and run the watch.
- Advance the crown through the calendar positions and confirm the date and moon disc respond as they should.
- Inspect the moon phase disc under a loupe: the moon and stars should have crisp edges, and the sky disc should be a deep even blue or a properly polished metal.
- Turn the watch over and study the movement finish through the caseback. Look for Geneva stripes that line up with the bridges, blued screws, and an engraved balance cock.
- Rest the watch and time how long it runs, then compare the result with the stated reserve on each indicator.
Testing the Moon Phase
A correct moon phase runs on a 59-tooth disc paired with the calendar train, which drifts by about one day every two and a half years. On a replica, the disc often advances with the date jumper instead of its own gearing, so the moon position slips out of step within weeks. Set the moon to full, note the date, and check the disc one week later. Month by month, the disc should move roughly one quarter of its cycle.
Common Flaws
- Printed moon disc instead of an applied or inlaid one
- Second power reserve indicator that is a decal and never moves
- Sweeping seconds hand instead of a jumping one
- Case thickness two or more millimeters off spec
- Date that changes at noon rather than at midnight
- Rotor that spins with a dry, rattling sound
Work through the steps in order, and the weak points show up before you commit. The jumping seconds and the twin reserve remain the hardest features to fake at any price.