The moonphase is one of the oldest complications in watchmaking and still one of the most loved. It does nothing you strictly need, and that is the point: a small window on the dial that follows the moon through the month turns a watch into something you look at for pleasure. This guide explains what the display shows, how it works and how to set it correctly.
What a moonphase display shows
Behind a curved aperture on the dial sits a rotating disc printed with two moons on a night-sky background. As the disc turns, one moon passes across the opening and the edges of the aperture hide and reveal it, mimicking the moon's phases: new, waxing, full, waning. Look at the window and you see roughly what you would see if you looked up at the sky that night.
How it works
A lunar month, from one full moon to the next, lasts about 29.5 days. On most watches the moon disc has 59 teeth and advances one step every day, so its two moons complete two full cycles in 59 days, an average of 29.5 days each. The real figure is 29.53 days, which means a standard moonphase drifts by about one day every two and a half years. For a mechanism you glance at rather than navigate by, that is more than accurate enough, and a quick reset brings it back in line.
How to set a moonphase watch in three steps
- Find the date of the most recent full moon. Any lunar calendar or a quick search will give you the date.
- Set the display to full moon. Advance the moonphase until the moon sits fully centred in the aperture. On Valuchi watches the moonphase is adjusted with the crown or a small corrector; your watch manual shows exactly which position to use.
- Advance one step for every day since that full moon. If the last full moon was six days ago, move the display forward six days. Done.
Two practical tips. If today is a full moon, step two is all you need. And on automatic (self-winding) watches, avoid adjusting any calendar function between roughly 9 pm and 3 am, when the date mechanism is engaged.
Model-specific instructions: Lunar Calendar manual, Lunar Calendar Automatic manual and Dual Calendar manual.
Moonphase, lunar calendar or dual calendar?
The names describe what sits around the moon window.
- Lunar Calendar 40mm: a full calendar display alongside the moonphase, powered by a quartz movement. The original Valuchi design.
- Lunar Calendar Automatic 40mm: the same calendar and moonphase layout, powered by a self-winding mechanical movement that runs on the motion of your wrist.
- Dual Calendar 40mm: date and weekday indicators with a moonphase, in classic, guilloché, Arabic and mosaic mother-of-pearl editions.
- Expedition 40mm: a square, sport-inspired moonphase with luminous hands.
- Clouds Edition and the KSA Women's Edition: 31mm women's moonphase watches with mother-of-pearl dials.
Which moonphase watch is right for you?
If you want the complication at its most accessible, start with the Lunar Calendar 40mm. If you like the idea of a watch with no battery, the Lunar Calendar Automatic is the one. For something rarer, the Dual Calendar Arabic, Mosaic and KSA editions are limited and numbered. And for a smaller wrist, the Clouds Edition brings the moonphase to a 31mm case.
Frequently asked questions
How accurate is a moonphase watch?
A standard 59-tooth moonphase drifts about one day every two and a half years. Resetting it takes a minute.
Does the moonphase keep running if I stop wearing the watch?
On a quartz watch, yes, as long as the battery lasts. On an automatic, the watch stops after its power reserve runs out, so you reset the time, calendar and moonphase when you put it back on.
Is a moonphase watch useful?
Practically, it tells you the phase of the moon at a glance, which matters for anyone who follows a lunar calendar. Emotionally, it is a daily reminder that the watch on your wrist is connected to something much larger.