Audemars Piguet Jules Audemars 25934BC 'Equation of Time'

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There’s complicated and there’s Complicated with a capital C. This Equation of Time Perpetual Calendar from the early 2000s is proof of Audemars Piguet’s rightful position at the pinnacle of mechanical watchmaking.

This complication is a bit complicated to explain, no pun intended. But, bear with us, for it’s truly impressive.

As watch lovers, we’re used to keeping track of the passage of time by conceiving of a 24 hour day, with each hour consisting of 60 minutes and, subsequently, each minute made up of 60 seconds. This timekeeping convention reflects the approximate time it takes for the Earth to complete one revolution around its own axis with respect to the Sun.

Yet, the actual time it takes for the Sun to reach its highest point in the sky two consecutive times varies per day. This is caused by the Earth revolving around the Sun in an elliptical orbit and because the Earth’s axis is tilted. As a result, almost all days in the year are slightly longer or shorter. In fact, throughout the year there are only four times where one revolution around the Earth’s own axis relative to the Sun corresponds exactly to 24 hours (in March, June, September, and December). The rest of the year, the maximum difference between ‘true solar time’ and the ‘mean solar time’ we use on a daily basis is between minus 16 minutes in November and plus 14 minutes in February.

An ingenious mechanism to indicate the difference between ‘true solar time’ and ‘mean solar time’, also known as an ‘equation of time’ complication, was implemented in a clock for the first time by Joseph Williamson in 1720 and, subsequently, in the twentieth century in a wristwatch.

The equation of time is one of the most romantic and metaphysical complications as it tracks the movement of Earth and humankind through time and space. Often paired with another astronomical complication—the perpetual calendar that tracks variances in the length of months and years—the equation of time is one of the true hallmarks of ultra-complicated watchmaking.

It is fitting that Audemars Piguet incorporated this complication into its haute horlogerie Jules Audemars line that was named after one of the company’s two founding fathers. The ref. 25934BC was introduced in the early 2000s and features a contemporary 39 mm case crafted from 18k white gold and a classic silver dial with an engraved circular pattern.

The 25934 implements the equation of time complication by means of a central hand with a lovely gold sun-shaped tip. The hand moves along a -14/+16 minute engraved scale on the bezel, allowing one to take note of the difference between the true and mean solar times. In classic style, the equation of time is combined with the perpetual calendar and moon phase complications, which are displayed on the sub-registers at the 6 and 12 o’clock positions. The astronomical theme is continued with the inclusion of two sub registers at the 3 and 9 o’clock positions that indicate the time at which the sun rises and sets.

This exceptional astronomical watch runs on a beautifully finished manual winding movement (which is visible through the sapphire case back) and comes on a black alligator leather Audemars Piguet strap with an 18k white gold AP-signed ardillon buckle.



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