The Perpetual Calendar - It will remain accurate until 2100

Perpetual calendars are among the most complicated watches that exist and are a true feat of miniaturization and engineering. A perpetual calendar watch accurately tells the day and date as long as they are kept wound, even accounting for leap years.

This means you won’t have to reset your calendar in months that don’t have 31 days. If wound, they will remain accurate until the year 2100, which should be a leap year but isn’t in order to account for the extra time that builds up due to the rounding a leap year requires. (You can read more about that here.) British watchmaker Thomas Mudge is credited with inventing the first perpetual calendar pocket watch in the 18th century, and Patek Philippe with the first wristwatch in 1925.

A perpetual calendar watch typically displays the day of the week, date, month, and year in the leap-year cycle. Many also include a moonphase. Watch brands use windows and subdials to indicate the calendar. Historically, perpetual calendar watches were classic, elegant dress watches. But, as more brands have mastered the perpetual calendar, there’s a wide range of watches out there that suit every style, including many bold, sporty timepieces.

Vacheron Constantin is one of the oldest and most prestigious watch brands in the world and is a master of perpetual calendars. It produces perpetual calendar watches in many of its collections, including the elegant Patrimony and Traditionnelle lines, where it recently introduced its first-ever women’s perpetual calendar watch, as well as the sporty Overseas collection.

Since it was revamped in 2016, the Overseas collection has expanded to include a host of complications, including dual time, chronograph, tourbillon, and ultra-thin perpetual calendars, some of which are skeletonized to show off the complicated and perfectly finished movement.

Vacheron Constantin recently introduced a 41.5mm pink gold model with a blue skeletonized dial, the Overseas Perpetual Calendar Ultra-thin Skeleton. All Overseas watches feature removable straps, and this watch is accompanied by blue leather and rubber straps to complement the dial.

Glancing at the subdials, you will notice that something seems to be missing. Where’s the leap-year cycle, and what’s happening with the month disk? Instead of including separate indications for the month and leap year, Vacheron Constantin opted to combine them by showing the first month in each quarter for four years. The leap year months are in blue font instead of white to distinguish them.

While it’s a little odd, it allows for a perfectly symmetrical design that includes all of the information in four subdials without needing to include two indications within one subdial or break the harmonious dial composition with a leap-year aperture.

Because the movement is skeletonized and has an open caseback with a peripheral rotor, you can admire the finely finished movement. It features a combination of satin- and circular-brushed, chamfered, and sunburst- or circular-grained decorations on the components. The mainplate, bridges, and rotor were treated with an NAC electrolytic treatment to give them a grey hue, which enhances contrast and visibility. The movement is so impressive that it won an award at the Grand Prix d’Horlogerie de Genève, considered the Academy Awards of the horological world.