The calibre Lange L001.1 by A. Lange & Söhne is installed in the A. Lange & Söhne Double Split. It is based on the calibre L951.1.

In addition to the rattrapante mechanism with the characteristic rattrapante pliers, for the first time a sophisticated lever system is used, which transmits the rattrapante function also to the minutes counter-axle. Only partially visible below, the chronograph, the flyback and the minutes counter mechanism are arranged. To minimize mechanical friction at the stopped rattrapante hands but still running chronograph, an insulator mechanism is used, which was newly developed by Lange and registered as patent.

The plates and bridges in untreated German silver are decorated with perlage and Glashütte Stripes, all edges are angled and polished. Likewise, the swan's neck spring and the two classical column shift gears.