A. Lange & Söhne - German watch, Wrist watch, mechanical movement, Glashutte, Chronograph, Tourbillon

Constant-force escapement
A mechanism integrated between the mainspring barrel and the going train in the LANGE 31. It assures constant torque delivery for an entire month and thus enhances the movement’s rate accuracy. A pretensioned, so-called remontoir spring is retensioned by 60 degrees every ten seconds. During the next ten-second period, it transmits this always constant amount of energy to the going train.

Twin mainspring barrel
Two barrels in tandem. Lange's twin mainspring barrels allow the implementation of a progressive power-reserve indication and deliver a power reserve of at least three days.

The world’s first mechanical wristwatch with a power reserve of 31 days and a | constant-force escapement that powers the going train with constant torque delivery. The tremendous amount of energy needed to keep the watch running so long is transferred to the movement with a winding key and stored in a | twin mainspring barrel.