What does “Annual Calendar” mean?

An annual calendar is a complication that shows the date (and often the day and month) and automatically accounts for months of 30 and 31 days, so it only needs correcting once a year, at the end of February. Patek Philippe introduced the first annual calendar wristwatch, reference 5035, in 1996. Rolex's Sky-Dweller uses its own annual calendar system, called Saros.

Annual calendars sit between a simple date and a perpetual calendar: more practical than a standard date, and simpler and usually less costly than a perpetual. Buyers should check that the date, day and month advance correctly, and should know how to set them, since adjusting a calendar at the wrong time of day can damage the mechanism on some watches. Service history matters, as calendar mechanisms add parts that need maintenance.

Example: 'Annual calendar, date and month set and working, full set.'