Auxanometer

An auxanometer (Gr. auxain, "to grow" + metron, "measure") is an apparatus for measuring increase or rate of growth in plants.

In case of an arc-auxanometer (see picture), there is a wire fixed with the plant apex on one end and a dead-weight on the other. It passes over a pulley which has a pointer attached to it. When the plant's height increases, the pulley rotates and the pointer moves on a circular scale to directly give the magnitude of growth.

Sensitive auxanometers allow measurement of growth as small as a micrometer, which allows measurement of growth in response to short-term changes in atmospheric composition. Auxanometers are used in laboratory, the field, and the classroom. It is also called an arc-indicator.