Day - Date

The day-date complication has its own place within the family of calendar indications. Most of the time, the day and the date are shown in apertures, although certain models opt for pointers (sometimes retrograde) on a subdial. Mechanically speaking, the day and date indications are driven by star wheels. The driving wheel for the days has 7 teeth whereas the driving wheel for the date has 31 teeth. They connect with the hour wheel through an intermediate wheel to advance by one increment every 24 hours. Without the intermediate wheel, they would advance at twice that speed.

Even complete calendars don’t have a perpetual day-date function. With a non-perpetual day-date, while the day will never need correcting, the date must be manually adjusted five times a year, at the end of months with less than 31 days, i.e. February, April, June, September and November.

A day-date function requires careful control of energy supply for the two indications to change simultaneously and every day. Depending on the degree of sophistication, the day and date change can be standard, semi-instantaneous or instantaneous. The most basic is the standard or direct-drive indication which is constantly engaged with the hour wheel and takes around two hours to change. The semi-instantaneous solution has a jumper (a flat spring) that rests between two teeth and is pushed by a pin or finger until it snaps the indication to the new position. The instantaneous solution, which is the most elaborate, gathers energy in a cam which is released seconds before midnight to push the indication forward.

Calendar functions appeared early on, and not just on clocks. Some seventeenth-century watches, such as the one made by Marc Girard in Blois or by Nourrisson in Lyon, already showed the date, the days of the week and moon phases.

In the early 1900s, manufacturers such as Alfred Lugrin in Vallée de Joux (future Lemania) or Ditisheim & Cie. in La Chaux-de-Fonds, not forgetting Volta, Vulcain and numerous other brands, began to produce calendar chronographs on an industrial scale. Patek Philippe made the first wrist calendar chronograph with day, date, month and moon phases in 1937. The Rolex Datejust, launched in 1945, became the first automatic waterproof wristwatch to show the date in an aperture at 3 o'clock. Legibility was improved in 1953 by the addition of the Cyclops lens. Rolex was also first to present a model with both date and instantaneous day display, spelled out in full in a curved aperture at 12 o'clock.

The aptly-named Day-Date was released in 1956 with a choice of twenty-six languages for the day. Confirmation of how useful this complication is, the Day-Date remains part of the brand's regular production. Today, numerous brands have their own day-date model, from luxury offerings such as the Blancpain Villeret Day-Date to the mass-market Swatch New Gent.