A computational masterpiece
The true solar day and the mean solar day are unequally long at least 361 days each year. An algorithm can be derived from their differences, and inventive watchmakers have programmed this algorithm into a kidney-shaped cam. Powered by the watch’s movement, this cam rotates through 360 degrees from January 1 to December 31 in order to indicate the equation of time. The first equation timepieces were made in the seventeenth century. One of the most famous is the so-called Marie Antoinette pocket watch, which its namesake ordered from Abraham-Louis Breguet in 1783. There are two fundamentally different systems for this additional function. One shows only the difference between true and mean solar time. The other is more convenient with an additional minute hand that points to the true solar time running alongside the minute hand. Breguet’s watchmakers chose this relatively complex system for their new Marine Équation Marchante 5887, whose automatic Caliber 581DR has much to offer. First, it has a one-minute tourbillon, an element invented by Abraham-Louis Breguet, in which the escapement revolves unobtrusively, yet visibly, within an aperture in the dial. The equation cam, which is secured to a transparent sapphire crystal disc with month indices, is more prominently visible. The cam delivers the necessary data to a hand that is identifiable with its stylized sun. Its indispensable scanning lever is visible in the upper portion of this window. A little differential gear serves as the link to the separate dial train. The third complication reveals its existence by the presence of windows for the day of the week, month, and leap-year cycle. This perpetual calendar will require no manual resetting until 2100, the next secular year. A retrograde hand – meaning that the hand leaps back to its starting point at month’s end – displays the date. The 16-line movement runs for 80 hours after
it has been fully wound, and the status of its power reserve is shown at the 7:30 position. Breguet makes the hairspring and some parts of the escapement for this caliber from silicon. Its variable inertia balance runs at a frequency of 4 Hz/28,800 beats per hour. Its 43 mm platinum case resists water pressure to ten bar.
Marine Équation MarchanteIn addition to the ordinary time of day or night, Breguet’s newest top-of-the-line model also indicates true solar time. A little sun is affixed to the tip of the hand for the equation of time, which varies cyclically throughout the year.
- Material: Platinum
- Caliber: Automatic, 581DPE
- Diameter: 43.9 mm
- Special features: Equation of time, perpetual calendar, one-minute tourbillon, water-resistant to 10 bar
- Wempe reference: BG220044