It only happens once every four years: February runs to an extra day, the 29th, making this an unusually long year of 366 days. These leap years, and 2016 is one, are the consequence of the time the Earth takes to rotate around the Sun. Rather than completing a revolution in precisely 365 days, our planet in fact takes 365.2422 days. So as to avoid the seasons falling out of sync, which is what would happen over a number of decades, the calendar intercalates one year every four years. Watchmakers have found their way around this phenomenon by inventing the perpetual calendar mechanism – sometimes referred to as QP from the French quantième perpétuel – which takes this additional day into account. For those whose wristwear includes a perpetual calendar complication, it’s business as usual today, February 29th 2016, with no need to adjust their watch. Thinking ahead to 2020, 2024, 2028, and so on, anyone else might want to take a look at these perpetual calendars by Audemars Piguet, H. Möser & Co, A. Lange & Söhne, MB&F and Vacheron Constantin.
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