Often called a ‘Grand Complication’, the Perpetual Calendar makes for an intriguing watch, especially when compared to its more affordable sibling, the Annual Calendar. The difference between perpetual and annual calendars is that the annual requires adjustment every year to account for the leap year while the perpetual has been designed specifically to solve this problem. (Sometimes a perpetual calendar will even include the year.) But at first glance, the two complications looks very much the same, both displaying the day, date, and month. So then, what makes the Patek Philippe Ref. 3940 a special watch?

The 3940 Perpetual Calendar is generally considered one of the most important pieces in modern Patek Philippe history and it is the watch Philippe Stern choses to wear every day. It was released alongside the venerable Ref. 3970 in a time when complicated watches were few and far between. A marvel in both design and craftsmanship, the 3940 wears incredibly thin due to its micro-rotor movement and very small but legible case. Patek showed great restraint when designing the watch, creating a masterpiece with a beautiful and classic symmetry to the dial along with a modern and forward-thinking movement.