Tracking the evolution of wristwatch calendar displays with iconic models

Among watch enthusiasts, the "aestheticians" who are always seeking beauty in mechanical watches say this: "A watch doesn't need a calendar display." They want to eliminate as many unnecessary elements as possible from the dial, and don't want to poke an unfashionable display window into a beautiful "canvas." Is this feeling getting stronger? Certainly, the more elements a watch has besides showing the time, the more practical its role as a tool becomes. But isn't that precisely why they want to seek even more beauty in the calendar display, which is such a practical function? Yes, it is precisely these practical functions that they want to be beautiful. This desire was embodied in the pursuit of the calendar display.

The Evolution of Calendar Displays

In a watch, all displays are regulated by the movement, which places great restrictions on their layout. One way to alleviate this restriction and make calendar mechanisms easier to read and more beautiful is to use a window display, which takes up less space than a subdial and hands. First used to display the date, the window display was eventually used to display the day of the week and month, modernizing the appearance of complex mechanisms such as perpetual calendars and annual calendars. The mechanism itself, which restricted design, became easier to use and offered greater freedom in layout with the invention of the "continuous type" using planetary gears.

Easy to see, easy to use, and beautiful

　Longtime watch fans may remember that the Rolex Datejust, launched in 1945, was once said to be the world's first watch with a window display calendar. However, in reality, attempts have been made to display calendars in windows using discs, rather than inset dials and hands, from a relatively early period, such as a pocket watch produced in Glashütte, Germany in 1890, which was equipped with a window display calendar. Nevertheless, the Datejust was called the "original" because it set the standard for models with a date display.

　Before its introduction, calendar mechanisms in wristwatches hadn't generated much interest. They were merely collector's items found only in certain luxury watches. The Datejust, which dared to incorporate one into a practical watch, was an unprecedented hit, contrary to most expectations. As a result, the date window at 3 o'clock that the Datejust adopted became the standard that continues to this day.

　The advantage of a window display is that it takes up less space on the dial than a pointer-type display, making it easier to organize the layout. This advantage was taken advantage of in the Day-Date, an advanced version of the Datejust that was born in 1956. In addition to the date window at 3 o'clock, it is equipped with a day window at 12 o'clock. What makes the Day-Date unique is that the day of the week is displayed in full. The day window is located on an arc between the 11 o'clock and 1 o'clock indexes, without disrupting the dial style that is so characteristic of Rolex.

　The aperture calendar, which became standard in the Datejust and Day-Date, began to be used in perpetual calendars in the late 1990s, where pointer-type calendars had previously been the norm. For perpetual calendars with many displays, aperture displays offer space-saving advantages and a more modern appearance. Furthermore, the Perpetual Ludovico, released by Ulysse Nardin in 1996, boasted superior mechanical capabilities. The date display was enlarged using two discs, and the month and day of the week were also displayed in apertures. Each calendar display allowed for both fast forward and reverse movement. Previous perpetual calendars used a main lever to operate gears that switched between calendar displays. The lever "pushes" the gears with a horizontal movement, preventing reverse movement. In contrast, Ulysse Nardin's perpetual calendar used a combination of planetary gears instead of levers to program long and short months and leap years. As a result, everything was controlled and driven solely by rotary motion, making reverse movement possible.

Cal.UN-32
The nested gear unit on the left is the programming wheel. Inside the large date wheel are two gears with different numbers of teeth that are driven by a planetary gear. The large date wheel and the two inner gears mesh with the 24-hour wheel on the right, adjusting to the length of the month and the end of February in leap years, and correctly advancing the date.

　Ulysse Nardin's "continuous" perpetual calendar using planetary gears also had a major influence on subsequent calendar mechanisms. Not only was it possible to reverse the time, but unlike lever-type calendars that require fine adjustment during assembly, the gears do not require adjustment, making assembly easier and allowing for greater freedom in positioning. This mechanism was designed by Dr. Ludwig Esculin, who also designed an annual calendar using the same planetary gears for an original watch at the La Chaux-de-Fonds (Museum International de Horlogerie de La Chaux-de-Fonds). This complex mechanism automatically determines the length of the month, except for those that fall on the last day of February. Dr. Esculin realized this with just nine parts, and it also features a day/night indicator.

　The design, which aligns the day, month, and day of the week apertures with the day/night indicator in a straight line, is as simple as the mechanism itself. It is a fine example of a contemporary calendar mechanism, and can be called a masterpiece.

The two illustrations show the annual calendar module added to the dial side. The annual calendar with day, month, and day of the week display and the day/night indicator are realized with just nine parts, including two planetary gears. Efforts have been made to reduce the number of parts, such as by using gears for each display disc.

A small window on the case back houses a disc-type chronograph 30-minute counter.