Blancpain's Villeret Equation du Temps ("Equation of Time") Marchante is a watchmaking masterpiece that integrates the rare and difficult running equation complication in the small dimensions of a wristwatch.
This exceptional mechanism measures the difference between the length of the actual solar day – solar time – and the 24-hour day – civil time. The accumulated differences between civil time and solar time can be as much as +14 minutes and -16 minutes; on four days per year the errors catch up and the solar time and civil time correspond exactly.
With the running equation movement, a second minutes-hand is added indicating solar time. This offers the advantage that the solar time can be directly read from the face of the watch. The difference can also be discerned from the difference between the solar minutes-hand and the conventional civil minutes-hand.