Illustration from 1911 Encyclopædia Britannica, article CALCULATING MACHINES.

Original text: Altogether different from the planimeters described is the hatchet planimeter, invented by Captain Prytz, a Dane, and made by Herr Hatchet planimeters. Cornelius Knudson in Copenhagen. It consists of a single rigid piece like fig. 16. The one end T is the tracer, the other Q has a sharp hatchet-like edge.

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