How to set a perpetual calendar watch

What it keeps track of

A perpetual calendar knows how long every month is and which years are leap years, so it shows the right date without correction until 2100, a year that is not a leap year. Most also show the day of the week and the month, many add a moonphase, and the leap year is a small hand or window marked 1 to 4 or L.

All of that depends on the watch running. If it stops, every display stops with it, and bringing it back means advancing each one to today.

Before you start

• Wind it fully, so it does not stop again halfway through.
• Find the correctors: small recessed pushers in the case side, pressed with the stylus that came with the watch or a wooden toothpick. Never a metal pin, which scratches the case and can slip.
• Some perpetual calendars, including IWC's, set everything by turning the crown forward instead. Read the manual first.
• Open the perpetual calendar helper: it shows what each hand should read today, and how many days the watch is behind.

Steps

1. Set the hands to about 6:30, well away from the hours around midnight.
2. Press the date corrector until the watch shows yesterday: one press fewer than the days it is behind. On most watches the month and leap year move with the date at the end of each month.
3. Check the month and leap-year hands. If yours has separate correctors for them, set them now.
4. Press the day-of-week corrector until it shows yesterday.
5. Set the moon with one press fewer than the helper gives. The moonphase guide explains how.
6. Turn the hands forward through midnight once. The date, day and moon all move on to today, and the watch is on the right half of the day. Carry on to the correct time and finish with the sync countdown to get the seconds.

Rules

• Never press a corrector between about 9pm and 4am on the watch, when the calendar is changing. The date check shows the window.
• Never turn the hands backwards unless the manual says it is allowed.
• Press firmly and fully, one press at a time. A half press may not register.
• If the watch has been stopped for many months, the presses add up. A watchmaker or the brand's service centre can set it for you, and some do it free.

Keeping it running

A perpetual calendar is the one watch where a winder really earns its place. Wear it often, or keep it on a winder, and it only needs you in 2100.