The only fake Duomètre moon phase worth considering is the one that runs a genuine 29.5-day lunar cycle on a complication train kept separate from the timekeeping train. Copies that rotate a sun-and-moon disc once every 24 hours are day/night indicators wearing moon phase clothing. That one distinction, plus aperture shape, subdial layout, case proportions, and movement finishing, is what separates a wearable first copy from a costume piece.

Why the moon phase is the giveaway

A moon phase is a gear ratio problem. The lunar disc sits behind the dial and advances one tooth per day on a wheel cut to finish a lunation in roughly 29 days and 12 hours. That means the disc steps forward once every 24 hours, and it does not care whether the sky outside is bright or dark. On a genuine moon phase, the moon sits in the aperture at noon just as calmly as at midnight.

Cheap fakes break this in an obvious way. The disc carries a sun on one half and a moon on the other, and it turns through a full revolution per day. Watch the aperture for a minute or two. If the disc creeps, you are looking at a day/night wheel. If it holds still, the mechanism is at least trying to be a moon phase.

Tier one: the 24-hour sun-and-moon copy

These are the watches that flood listing pages at the lowest prices. The dial prints a moon and stars, the aperture sits roughly where it should, and the effect falls apart the moment anyone looks closely.

  • Pros: inexpensive, keeps time, light on the wrist, no winding routine.
  • Pros: fine for a display shelf or a costume.
  • Cons: disc cycles daily instead of monthly, so the moon is wrong most of the day.
  • Cons: ticking quartz seconds hand, flat caseback, thickness that does not match the real silhouette.
  • Cons: printed subdials rather than working ones.

Best for: someone who wants the shape on a shelf and never intends to hand the watch to another enthusiast.

Tier two: automatic with a true lunar disc

This is the practical middle. The movement is mechanical, the sweep is smooth, and the moon disc advances on a lunar wheel rather than a daily wheel. Subdial placement usually follows the original layout, and the case finishing holds up in normal conversation distance.

  • Pros: correct 29.5-day lunation, so the aperture reads right for weeks at a time.
  • Pros: mechanical sweep, decent crown action, believable dial furniture.
  • Cons: the lunar disc is often slaved to the hour train instead of running on its own reserve.
  • Cons: a power reserve indicator, where present, may be decorative and never move.
  • Cons: bridge finishing looks stamped rather than striped under a loupe.

Best for: daily wear where the watch is seen on the wrist and handled only by the person wearing it.

Tier three: custom build with an independent complication train

The Duomètre line is built around a dual-wing idea, where the timekeeping function and the complication run on separate gear trains with separate power reserves. A custom copy that mirrors this is a different class of object: the complication keeps its own rate, and the going train is not dragged down by it.

  • Pros: independent complication train, so the moon phase is not a passenger on the hour wheel.
  • Pros: closer case proportions, better hand finishing, correct aperture geometry.
  • Cons: higher cost, longer lead times, harder to service locally.
  • Cons: still not the original, and should never be represented as one.

Best for: collectors who understand exactly what they are buying and want the architecture, not just the look.

Case and dial checks that matter

Measure the case against published figures before you commit, because fake cases drift wide and thick. Check that the lugs curve rather than cut straight down, that the crown is properly signed, and that the dial printing is crisp under magnification. On the moon aperture, the opening should be circular with the disc seated flush behind it. If the disc sits proud of the dial, it is a decal or a stamped plate.

Questions to ask before you buy

  1. How many days does the moon disc take to complete one cycle?
  2. Is the moon phase driven by the hour train or by a separate wheel?
  3. Does the power reserve indicator actually move?
  4. What are the case diameter, thickness, and lug width?
  5. Can you send a short video of the aperture over a full day?

A seller who answers these with specifics is selling a watch. A seller who answers with adjectives is selling a photograph.

Bottom line

If the moon disc does not track a real lunation, nothing else about the watch matters. Buy the tier that matches how the watch will actually be used: shelf piece, daily wearer, or architecture-driven custom build. Pay for the mechanism, not the story.