In this post we talk about perpetual calendars in watches. This nifty function keeps track of days all year for you, so you don’t have to adjust the date every month. Even more, it will keep the leap years, adjusting to include the day of Feb 29th every four years. We’ll touch on the topic of what leap years are, and on the not very well known fact that some years that are supposed to be leap years, in actual fact aren’t. This goes against the principle, but it has some practical purposes.