Resistograph

Resistograph is a mechanical resistance measurement device, developed by Frank Rinn (since 1986 in Heidelberg, Germany).
Driven by a drill motor, a long, thin needle is inserted into a wood log or structural wood beam in order to gain an idea of its density, often to identify areas of substandard structural integrity such as decay. Variations in resistance to torque are recorded by a stylus on graph paper. Newer models may record information digitally but the purpose of the instrument is the same.