Difference between true solar time and mean solar time. True solar time is measured by sundials while local mean solar time is no longer used. In the past, it was measured by clocks mounted on public buildings. It was calculated by adding the positive or negative equation of time, as recorded in tables, to the time indicated by sundials.Today, mean solar time is that of an entire continent (Central European Time).Mathematicians have a rendezvous with the sun four times a year. This is when mean time (that of our watches) and true solar time (that of sundials) coincide.The equation of time is the difference between true solar time and mean time. True solar time, as displayed by sundials, varies from day to day on account of the Earth's elliptical orbit. It also varies according to the longitude of the point of observation.Mean time, as displayed by watches, ignores these variations and, whatever the day of the year, mathematically divides time into minutes of 60 secondsFour times a year, on 15 April, 14 June, 1 September and 24 December, mean time and true solar time coincide. Between these dates, the deviation ranges from -16 minutes and 23 seconds on November 4th to +14 minutes and 22 seconds on February 11th.In 2000, Audemars Piguet unveiled a wrist watch combining the three equation of time functions: sunrise and sunset time and perpetual calendar. The equation of time hand gives an accurate reading of this daily variation. Catch A projection of a part, wheel or lever which generally hooks, releases or locks a mechanism.