The perpetual calendar presents a mechanical solution for an astronomical problem. Gears, springs and rockers mimic the rotation of the earth around the sun. The mechanism automatically knows whether the month has 28, 30 or 31 days, as well as calculating leap years. The perpetual calendar only needs correcting at the turn of each century, unless the century is divisible by four hundred.

Complete calendar watches measure the day of the week, month, and date. Certain models, such as the Fiftysix Complete Calendar, also display moon phases. These timepieces must be manually adjusted five times a year – in February, April, June, September, and November.

Annual calendar watches feature full or partial calendars that automatically account for months with 31 and 30 days. You must adjust these watches only once a year to account for the 28 days in February, except for leap year.

Moon-phase watches are timepieces indicating the evolution of the lunar cycle (new moon, first quarter, full moon, last quarter). These watches are distinguished by an additional wheel fitted next to their pinion and serving to mark off a cycle lasting 29 days, 12 hours and 45 minutes. They thus generate a discrepancy of just 57 seconds per lunar cycle, meaning less than 2 seconds a day. Manual adjustment of Vacheron Constantin moon-phase watches is thus required only once in every 122 years for high-precision moon-phase displays, and once every three years for simple moon-phase versions.