AN AVERAGE CALLER'S HEAD
The Engineer, 1966, C.C. Furnas & Joe McCarty, Eds.
More human-factors engineering
has gone into the telephone than into any other non-military device. For
example, when engineers were working on a new telephone handset in 1937
they measured 2,000 male and female heads before arriving at a diagram...showing
the average-sized human head. Later the handset was given slightly greater
curvature and shortened by about one half inch to bring the mouthpiece
closer to the average caller's mouth.
