If you ever thought that an 8-day power reserve was impressive, the A. LAnge & Söhne Lange 31 is the first mechanical wristwatch with a power reserve of 31 days. Yes, this exceptional timepiece will run for a whole month when fully wound so that rotate timepieces in your collection as frequently as you want without losing a single beat or having to set your calendar because your timepiece stopped while wearing other watches in your collection. Additionally, the A. Lange & Söhne Lange 31 it features a patented constant-force escapement, which makes it possible for the first time to actually harness such an extreme power reserve. This mechanism assures high rate stability and thus consistent rate accuracy for an entire month.