The Breguet Marine Équation Marchante 5887 features one of the most
rare and fascinating. It indicates mean solar time - civil hours and minutes - as opposed to true solar time - solar hours and minutes - by means of two separate hands. The marching solar hand, decorated with a facetted golden sun, offers direct indication of the minutes of solar time, a great time-saving convenience. This apparent simplicity actually conceals a sophisticated achievement, which few watchmakers are able to accomplish. In fact, the solar minute hand must respond to two imperatives: it must march conventionally across the dial, just like the civil minute hand, but it must move away from the latter by a variable value each day according to the analemma to indicate the equation of time. Breguet has achieved this by equipping the running solar hand with a differential gear, driven by two sources of rotation operating completely independently; the rotation of the civil minutes and that controlled by the lever in contact with the equation cam, which in turn makes one revolution per year. Breguet has developed an extremely fine equation cam, supported by a transparent sapphire disc, which also serves to correct the monthly time equation.
Adding to the complexity of the display of the marching equation is a perpetual calendar. Two windows, located between 10 and 11 o'clock and between 1 and 2 o'clock respectively, indicate the days of the week and months and the leap year. The date window is located inside the hour circle and is indicated by a retrograde hand. The automatic 581DR calibre is also equipped with a 60-second touribillon with silicon balance spring.
It is made of rose gold or platinum.
