The design of the perpetual calendar was a feat of watchmaking genius that finally paved the way for IWC’s entry into the world of Haute Horlogerie. A mechanical masterpiece, it takes into account all the complexities of the leap years; in other words, it recognises all the years that can be divided, without remainder, by four (e. g. 2012), as well as the centuries that can be divided, likewise without remainder, by 400 (e. g. 2400). These leap years all have a 29th day in February. Years at the turn of the century that leave a remainder when divided by 400 – the next ones are 2100, 2200 and 2300 – are not leap years. In cases like these, calendars with an analogue display will need to be advanced by 1 day on 1 March by a watchmaker. Calendars with a digital display can be adjusted by the owner. The perpetual calendar’s century slide with an analogue display turns each new century into a major event. The current century slide bears the numbers 20, 21 and 22 and will thus come to the end of its service life on 31 December 2299; but even now, IWC supplies the century slide bearing the figures 22, 23 and 24 for the years 2200 to 2499.