Cal. L101.1 was introduced in 2013 and is used in the A. Lange & Söhne 1815 Rattrapante Perpetual Calendar. It is a rattrapante chronograph movement with two column wheels. Additionally, it has subdial seconds and a perpetual calendar. The movement features 43 jewels and 4 chatons. The Lange in-house balance spring adjusts using screws and operates at 21,600 A/h.