Simple Education: Easy Guide To Understanding a Perpetual Calendar

We often get reader comments and questions about a variety of complications. While we understand that many of our readers are avid watch collectors, some are also novices. As such, we are implementing a monthly “Simple Education” column that will offer an easy guide to a variety of complexities in watchmaking. If you’re advanced, no need to continue, but if you want to learn something as a newbie to watches, read on as we present an Easy Guide to Understanding Perpetual Calendars.

What the Perpetual Calendar Offers

Sometimes referred to in French as the Quantieme Perpetuel, a perpetual calendar watch is a mechanical timepiece that tracks a wealth of calendar information and properly displays it. That information typically includes day of the week, date of the month, leap years, and moon phases. The most important thing to understand about a perpetual calendar watch (versus an annual calendar, for instance) is that the mechanics inside the watch accurately track and portray automatically the exact date of the month, whether the month has 28, 30 or 31 days in it. It even accounts for leap year.

How  the Perpetual Calendar Works

Understand that there are many different perpetual calendar watches on the market, and, by extension, the movements operate a bit differently from one to the next. However, essentially, most perpetual calendars today are built to track time until the year 2100, when they will need to be opened and readjusted by a watchmaker (ideally on March 1). The reason for this is simple: in the year 2100, when the leap year should occur, we will be skipping leap year in order to have real time (according to the Gregorian calendar) and solar time coincide correctly. The most important thing to know is that if a customer buys a perpetual calendar watch today, it doesn’t need an adjustment for 83 years.

Perpetual calendars are, by nature, extremely complex and typically hold hundreds of tiny mechanical parts inside. Most consist of a date wheel, a date change lever, a day wheel and a day-of-the-week lever, as well as month wheels and racks to make all of the parts engage and track time correctly. If the watch has a moonphase indication it will have yet another disk. Because of the extensive work that goes into building one, they generally command higher prices than simple watches.

Essentially, the perpetual calendar of today has its roots that date back to the late 16th century. Taking their inspiration from astronomical clocks and bell towers of the 15th and 16th centuries, watchmakers made small strides in incorporating the calendar function into portable timepieces. Over the ensuing centuries various calendar approaches appeared in the world of watchmaking. Today, the perpetual calendar is particularly popular thanks to its functions, as well as its beautiful design.