Esembl-O-Graf Vol. 1: Landeron Cal. 51 Chronograph

First published in 1949 by the Western Pennsylvania Horological Institute, the Esembl-O-Graf series was the first fully illustrated text on chronograph repair and remained a standard reference for postwar American watchmakers. Volume 1 covers the Landeron Cal. 51, a cam-and-lever chronograph that powered countless mid-century wrist chronographs from the late 1940s through the 1960s.

Authored by William O. Smith and his son William O. Smith, Jr.—respectively the Institute’s President and its Chief Engineer—the book walks through the chronograph mechanism one part at a time. Each part receives a fixed six-point treatment: disassembly procedure, hazards in disassembly, assembly procedure, hazards in assembly, function of the part, and remarks. Facing every entry is an isometric drawing of the part, a photograph of the assembled movement with that single part painted black to fix its location, the screw profile, and oiling instructions. A dedicated section on eccentric studs spells out which depthings each adjuster controls, followed by a functional check at the end.

A practical bench reference for anyone servicing a Landeron 51, and a useful template for thinking through any cam-and-lever chronograph.