The LANGE 31 is the world’s first mechanical wristwatch with a power reserve of 31 days and a patented constant-force escapement. To deliver a power reserve of this magnitude, the movement must be able to store a large amount of energy. This task is handled by two mainsprings that are both 1850 millimetres long – about ten times as long as in mechanical wristwatches with a conventional power reserve.

Mainsprings of this length imposed considerable challenges on the engineers. The first obstacle was to transmit their tremendous energy to the movement in a gentle and uniform manner. For this purpose, they developed a patented constant-force escapement. The second challenge presents itself when winding the watch, a very time-consuming and cumbersome task, given the length of the springs. This is why the LANGE 31 is wound with a key. It generates much more leverage than a winding mechanism based on a crown.