Audemars Piguet, “Jules Audemars, Equation du Temps” The “Jules Audemars, Equation of Time” was introduced into the market in 2000 and incorporates a perpetual calendar with leap year indicator. This complicated wristwatch mechanically tracks the time of sunrise and sunset for the designated city indicated on the bezel or around the dial under the crystal glass, and accurately shows the difference between mean solar time and sidereal time. The “Equation of Time” and its 423 components is another example for Audemars Piguet’s dedication to the art of fine watchmaking. The equation of time is the difference between true solar time and mean time: true solar time, given by sundials, varies from day to day because of the Earth's elliptical orbit, and according to the longitude of the point of observation. Mean time, given by watches, ignores these variations and for every day of the year mathematically divides time into equal hours. Produced in a limited quantity each year since 2000. Since the 2010’s, a “Royal Oak” version is also available. Equation of time An equation of time watch shows the difference between “true” solar time (that of Nature) and “mean” solar time (that of Man). This rare horological complication is usually combined with other “astronomical” indications. The Earth makes an elliptical orbit around the Sun; also, its axis is tilted from perpendicular to the plane of the equator. For these two reasons, a “true” solar day, which is the interval of time between two “true” noons when the Sun is at its highest point in the sky, is never the same length over the course of the year. It’s exactly 24 hours long on just four days: April 15th, June 14th, September 1st and December 24th. In an unchanging cycle, all the other days are either longer or shorter. This difference, which ranges from less 16 minutes and 23 seconds on November 4th to plus 14 minutes and 22 seconds on February 11th, is the “equation of time”. Watchmakers have always vied to find ingenious ways to convey these celestial mechanics. Because these variations occur identically on the same dates, they can be “programmed” by means of a cam making one complete rotation each year. This extremely sophisticated horological complication first appeared on long-case clocks. It was then miniaturised to fit inside a pocket watch and later, in the 20th century, a wristwatch. Rarely seen alone, the equation of time is a “classic” feature of any “ultra-complicated” watch. There are different ways to show the equation of time. Most watches prefer a hand sweeping a subsidiary dial or arc, graduated from 16 to + 14 minutes. This requires a little mental arithmetic by the wearer, adding or subtracting to calculate true time from mean time. Simpler to use but more complex to make, the “running equation” (équation marchante) has two coaxial minute hands, one to show mean solar time and the other true solar time at a glance. For many years this sophisticated system was found only on pocket watches, although the first wristwatches with running equation were recently unveiled. On the subject of innovations, watchmakers have devised systems for reading the equation of time at a specific longitude and not for an entire time zone, thereby further enhancing precision. Sunrise and Sunset Period between the rising and setting of the Sun. A 24-hour interval, determined by the Earth’s rotation on its axis.