Cal. L901.0 is one of the original watch movements produced by A. Lange & Söhne in 1994. It is a hand-winding movement with big date and power reserve used in the first Lange 1 models. This movement, more than any other, established the reputation of the new A. Lange & Söhne brand.
Cal. L901.0 features an offset dial for hour and minute hands, shifted towards 9:00, allowing space for a big date at 1:00, power reserve pointer at 3:00, and small seconds at 5:00. This novel dial arrangement has since become a signature of A. Lange & Söhne and is instantly recognizable in the watch industry. The big date complication was designed to resemble that of the Semper Opera House in Dresden, and was the first patent registered by the new company.
As is typical of A. Lange & Söhne watches, and reflective of the history of Glashütte watchmaking, the movement features a single large plate covering most of the gears, commonly called a Glashütte Three-Quarters Plate. To aid assembly, gold chatons provide access to the pivot points for the wheel train. A hand-carved balance cock features a swan neck regulator.