Landeron 51

The Landeron Cal. 51 is a cam-switching chronograph movement from the Cal. 48 family, introduced in 1947. It features a distinctive 'boot-shaped' hammer design that replaced the curved hammer of the original Cal. 48. Unlike most movements in the family, Cal. 51 uses a traditional horizontal clutch rather than an oscillating pinion to activate the chronograph function. The movement was updated around 1950 with a new hammer and cam mechanism. Related calibers include the 55 (14 ligne), 151, and calendar variants 59, 80, 81.