Like many great watchmakers, Abraham-Louis Breguet was fascinated by the subject and indication of the equation of time. Every watch that left his workshop demonstrated his desire to improve and perfect horology. Together with his son, Antoine-Louis Breguet, he manufactured fifteen equation of time watches between 1790 and 1830.

Building on the tradition started by Breguet over two hundred years ago, the present watch takes this complication even further by adding a perpetual calendar complication with an automatic movement, patented in 1991.

Equation of Time
A watch with an equation of time complication shows the difference between "true" solar time and "mean" solar time. The "mean" solar time refers to common time, based on a conventional twenty-four hour period, while "true" solar time actually varies with the earth's irregular orbit around the sun. These two times match precisely only four days each year.

The equation of time in astronomy is the quantity that needs to be added or subtracted to switch from real time given by the sun, to the mean time; our time, which arbitrarily divided a day in 24 hours. The equation of time varies from one day to another, its value swings between around -16 to +16 seconds per day. By cumulating these differences, we obtain a variation between the real noon and the mean noon of more or less 15 minutes. The most important differences are, function of the years, toward February 12 (+14 minutes and 59 seconds) and November 3 (-16 minutes and 15 seconds). The difference is zero toward April 15, June 15, September 1 and December 24.

In this day and age, the equation of time complication is a rare feature on a fine complicated watch. For the appreciator of clock and watchmaking history, a timepiece that highlights the equation of time is an opportunity to own a rare and romantic watch.

The "Equation of Time" model is illustrated in Breguet - Watchmakers since 1775 by Emmanuel Breguet, p. 175.