Cal. 48 is one of a family of chronograph movements produced by Landeron from 1937 through the 1970. In all, over 3.5 million examples were produced.
It is a 13.75 ligne movement with a cam switching chronograph system. a variety of 14 ligne variants were produced, as well as complicated versions with calendars, moon phase, and hour counters.
The preceding Landeron 47 movement (the first cam-actuated chronograph) featured three buttons Start, stop, and reset. Cal. 48 switched to two-button operation. But unlike most modern chronographs, where start/stop share a single button, Cal. 48 has one button (at 2 00) to start and a second (at 4 00) to stop and reset. A later revision of this movement, resulting in Cal. 149/189/349, features conventional start/stop button operation.
The original Landeron 48 featured a deep, curving hammer, a feature carried on to the 54, 56, and 58. The Landeron 51/151 features a conventional “boot” hammer, as does the 55, 57, 59/159, 80/180, and 81/181. The Landeron 148 moved to a distinct “JI” hammer shape, a feature shared by the 149/189/349, 154, 185, 186, and 187/248. Finally, the Landeron 152/352 moved to a deeply bowed hammer, a feature shared by the 153/353.