Dates and Calendars - The Other Measurements of Time

There’s a smorgasbord of complications for mechanical watches, many going back hundreds of years. For example, the tourbillon was invented in the late 1700s, while the minute repeater goes back another century. Both are still difficult to produce and remain very expensive. On the other end, the date is arguably the most useful complication and usually inexpensive, while additional calendars complete the overall measurement of time. In wristwatches, the first (production) date window appeared in 1915 in a Movado watch, although they existed in pocket watches a century earlier. Calendars go back even further, with the complex perpetual calendar appearing in 1762.

The modern calendar was established by Pope Gregory XIII in 1582, slightly updating the Julian Calendar. Named after him, this Gregorian calendar measures a standard year and became official in the United Kingdom and US colonies in 1751 (and as late as the 20th century in China and other nations). Let’s look at all the ways a watch can relay calendar information.

Date

The date is the most common and inexpensive complication, rarely adding much (if anything) to the cost of a watch. There are exceptions, however, such as big date complications that use twin date wheels to display each digit. The simple function shows the date of the month and most require a manual adjustment for months ending in 30 days (they go to 31 days automatically) and February’s shorter month. There are multiple ways to display the date with the most common being within a window at 3 o’clock, popularized by Rolex and the Datejust in 1945. Date windows can appear just about anywhere on a dial, however, such as 6 or 9 o’clock, or even angled between 4 and 5 o’clock on busy dials. Although a simple complication, some watches expose the date wheel to add a bit of engineering grandeur.

Pointer Date

A pointer date bypasses a window and uses an additional hand to point to the current number, usually printed around the perimeter of the dial. This predates the more common date window and is less common today, although brands like Oris have continued to embrace the style. A benefit of this is the lack of a dial disruption with a window, but it’s also not as intuitive to quickly see the date. Pointer dates can exist within a sub-dial as well, creating a stylish alternative to standard date windows.

Big Date

As mentioned, a big date enlarges the typical date window by using two separate wheels for each digit - a smaller one with 0 to 3 and a larger one with 0 to 9. This is more complex to produce and requires incredible precision for the numbers to perfectly align. The advantage is a larger, easier to see date window, but it comes at a cost compared to standard date displays. Horage pieces like the Autark and Array series and 40mm Omnium have big date complications, run by our in-house K1 automatic.

Day-Date

Day-dates have a separate window to show the day of the week, either next to the date window or elsewhere on the dial (often at 12 o’clock with the date at 3 o’clock). Arguably the best known day-date series is from Rolex, first introduced in 1956. You’d be surprised at how many day-date watches there are, however, from many different brands - Tissot, Seiko, Longines, Oris, Omega, Patek Philippe and more. Some come with more advanced engineering, such as an annual calendar, but more on that below.

Perpetual Calendar

Perpetual calendars almost never need to be corrected as long as the movement continuously runs. They’re generally accurate for 100 years, needing an adjustment at the start of a new century. In practice, however, it’s a bit of a moot point as watches never run continuously for a century, not to mention needing to be stopped for servicing. These typically show the date, day and month, and adjust for 30/31 days and February’s shorter month (including leap years). A moon phase complication is usually integrated with perpetual calendars, making them complete or full calendars. Full calendars, however, aren’t always perpetual calendars and vice versa. Invented by English watchmaker Thomas Mudge in 1762, it remained a rare pocket watch complication until Patek Philippe patented it for a wristwatch in the early 20th century. They have a mechanical “memory” that covers 1461 days. These remain expensive complications, usually reserved for a handful of luxury brands. A percentage of perpetual calendar watches use modules from Dubois Depraz, while others have very unique ways to display the calendar with in-house developments.  

Annual Calendar

As the name suggests, annual calendars need to be adjusted once per year in February. Although simpler than perpetual calendars, it was actually invented later. Much later, in fact, by Patek Philippe in 1996 as it introduced a complex yet more affordable movement. Unlike perpetual calendars, annual calendars often show the month and date only, and some even combine a date window with a pointer for the month (like Omega’s Globemaster). Although among the most recent mechanical developments, annual calendars have spread throughout the industry with brands like Longines, Rolex, Omega, Blancpain, Audemars Piguet and many more embracing the complication.

This doesn’t cover all possible calendar configurations for mechanical watches, but it does hit on the majority. Dates and calendars are the perfect complement to watches as they complete the measurement of time beyond hours, minutes and seconds with days, weeks, months and years.

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Erik Slaven