Perpetual calendar

A perpetual calendar is a complication that shows the date, and usually the day, month, and leap-year cycle, and adjusts automatically for months of different lengths and for leap years.

It's one of the most complex and valued complications, and perpetual calendars can command high prices. They're also costly to service and can be damaged by incorrect setting.

If a perpetual calendar has stopped, resetting it correctly may need a watchmaker. Check its functions and service history carefully before buying.