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Watch functions explained: How a perpetual calendar works

Leap Year

2016 was a leap year. That means February lasted 29 days instead of 28 days. Great, a whole day extra! But it usually means that on March 1st you have to manually put your watch on the right date. Did you know that there are also watches that do not need that?

In most analog watches there is a date disk that counts from 1 to 31 so the disc must be manually rotated 1 or 2 days further when the month takes only 30 (or in this case 29) days. Little effort, but something that you could forget very easily. There are also watches that are always on the right date.

How a perpetual calendar works


The perpetual calendar is one of the if not the most useful and romantic complication in the world of watches. Many watches have some sort of date indication, usually it’s the classic small window in the dial displaying the day of the month. Some watches even have a day of the week display as well.

The perpetual calendar has both, plus it only needs to be adjusted once a century. A perpetual calendar can track the date, day of the week, month, year, leap year, and in rare cases even the century and millennium.

A common analog watch with a perpetual calendar contains a complex clock wheel running several times per second or only once every four years. Most 'perpetual' calendars only need to be adjusted in the year 2100 at the earliest - leap years are skipped at the turn of a century, so the normal mechanical calculations require a tiny push forward at the end of February.

Most perpetual calendar watches are typically elegant and classic, which you might attribute to their usually high price tags, and the perpetual calendar chronographs from Patek Philippe are some of the most sought after watches of all time.