The revolutionary Lange 31 is the first mechanical wristwatch with a power reserve of 31 days. The exceptionally high power reserve can assure high rate stability and consistent rate accuracy for an entire month. The watch features the same key winding system as a historic pocket watch and can be wound with a stainless steel winding key through an aperture in the case back thus generating much more torque than would be possible with a crown. In order to prevent over tightening of the springs, this complex movement features a built-in torque limiting mechanism and a backstop ratchet that slows down the key when it is turned anti-clockwise.

The Lange 31 attests to the fine craftsmanship, technical excellence as well as aesthetic qualities at A. Lange & Söhne, making it a highly sought-after collector's watch.