How to set a moonphase watch
To set a moonphase, find out how many days it has been since the last full moon, advance the moon disc until the moon sits exactly at its full position, then advance it by that number of days. Do it outside the watch's "danger zone" (usually the hours around midnight, when the date is changing), and the moonphase will stay in step with the sky for years.
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Before you start
- Check the manual. Every movement is slightly different. Your manual will tell you how the moonphase is corrected (usually a small pusher in the side of the case, or a crown position) and when not to adjust it.
- Find today's moon age. Look up the date of the most recent full moon in a moon calendar, then count the days since. The lunar cycle is about 29.5 days.
- Avoid the danger zone. On many watches, using the correctors between roughly 9 pm and 3 am, while the date mechanism is engaged, can damage the movement. Set the time to around 6 am or 6 pm first.
Setting it, step by step
- 01Set the time to a safe hour, such as 6:00, away from midnight.
- 02Advance the moonphase until the moon is exactly "full": centred in the aperture. Each push of the corrector usually advances it by one day.
- 03Count forward the days since the last full moon, pressing the corrector once per day.
- 04Set the date, then the time. Check whether it's morning or afternoon so the date changes at midnight, not midday.
If your watch makes it easier to start from a new moon (an empty aperture), the same method works: centre the new moon, then count the days since the last new moon.
How accurate is a moonphase?
Most moonphase watches use a disc that drifts by about one day every two and a half to three years, so they need a small correction now and then. High-precision moonphases are accurate to one day in a century or more.
Did it stop?
If your watch has stopped, the moonphase will be behind. Wind it, then set it again from the last full moon. A moonphase is a good reason to keep a watch running on a winder, or to wear it regularly.
A helping hand
WristLog.app includes a moonphase tool that helps you work out the right position for today, along with a world-time helper for travel watches, so setting your complications doesn't mean digging out a moon calendar.
Common questions
Can I damage my watch setting the moonphase?
You can, if you use the corrector while the date-change mechanism is engaged, usually in the hours around midnight. Set the time to around 6:00 before correcting, and check your manual.
Why is my moonphase wrong after a few years?
Most moonphase displays approximate the 29.5-day lunar cycle and drift by about a day every two and a half to three years. A quick correction gets it back in step.
Do I need to set the moonphase every time the watch stops?
Yes, on a mechanical watch: the moonphase stops with the movement, so advance it by the days it was stopped (or reset it from the last full moon) along with the date and time.
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