What Makes a Perpetual Calendar Perpetual?
The date wheel on a modern watch is an extremely handy, albeit not foolproof complication. With many terms used by various manufacturers - date, quickset date, annual calendar, perpetual calendar - we wanted to take a few minutes to break down the various date complication types.
WHAT IS A DATE COMPLICATION?
It was in 1945 that Hans Wilsdorf introduced the Rolex Datejust to the world. Date displays had existed in several forms on watches prior, but it was the Datejust that claimed to be the first automatic changing date. It was this release that launched the modern date complication as we know it today: a hand or date window that indicates today’s date and increments every 24 hours.
Anyone who has owned a vintage timepiece can attest to the challenges of a date wheel that doesn't have a “quickset feature.” Introduced later as an improvement to the date complication, a quickset date function allows one to advance the date by adjusting the crown, pressing an adjustment pusher, or a number of other novel methods.
Quickset or not, the limitations of a traditional date complication is that the watch cannot automatically accommodate months with fewer than 31 days. For those months, the wearer is required to complain audibly while adjusting their watch to the 1st of the month. It is to overcome this arduous task that drove the creation of an annual calendar.
WHAT IS IN AN ANNUAL CALENDAR?
An annual calendar watch complication understands both the month and the date. When reaching the end of a 30-day month, an annual calendar will skip the 31st day on the date wheel and move to the next month.
The annual calendar is a complication that actually existed in some very limited forms dating back to the early 1900s, but only in bespoke commission timepieces by Patek Philippe and Breguet. More mainstream support for an annual calendar wouldn’t exist until the 1960s, and even then, the complexity relegated it to higher-end watches.
Lest you think that the annual calendar will solve all your manual date-adjusting woes, these movements generally only account for 30-day and 31-day months. February will still require the manual change from 28 or 29 into the 1st of March.
One notable example of an annual calendar is the Rolex Sky-Dweller. Holding the title for the Rolex watch with the most complications, the Sky-Dweller is both an annual calendar as well as a GMT-style watch for tracking a second time zone.
WHAT IS A PERPETUAL CALENDAR?
A perpetual calendar expands upon the features of the annual calendar by correctly handling the leap year process. To do that, the perpetual calendar must know the month, date, and the current year’s position in the four-year leap year rotation.
This expanded complication frees the user from concerns over month adjustments until the year 2100. In February 2100, the Gregorian calendar skips a leap year, as it does every 100 years.
Each of these subsequent additions expands upon the complexity inside the watch movement. For most watch owners, the traditional date complication with quickset is installed. To date, annual and perpetual calendars make up a very small percentage of overall date watch sales.
If nothing else, this semi-monthly adjustment gives us the opportunity to remove our watch, give it a few quick winds, perform a date change, and take a moment to appreciate everything that goes into its complex construction.
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