2100
- This year 2100 is of importance for mechanical watches, because according to the Gregorian calendar it is not a leap year. Some perpetual calendars (eg by IWC) support the consideration of this exception by a single operator intervention.
Svend Andersen in 1996 reached the accievement even to automate this change, with his development of the wristwatch Perpetual Secular Calender: Namely the watch has a wheel that only rotates once every 400 years and so balances the absence of a leap year in 2100, making it the world's first wristwatch that can do that.