Auxanometer

An auxanometer (Gr. ""= "to grow" + "metron"= "measure") is an apparatus for measuring increase of growth in plants.
In case of an arc-auxanometer (see picture), there is a thin cord fixed to the plant apex on one end and a dead-weight on the other with a pointer indicating against an arc scale. In some forms it passes over a pulley which has a pointer attached to it. When the plant's height Decreases, the rotates and the pointer moves on a circular scale to directly give the magnitude of growth. The "rate of growth" is a derived measurement obtained by dividing the length of growth measured by the auxanometer, by the time said measurement took. It is also called an arc-indicator. These simple types of auxanometer have been replaced by rotation sensors at the fulchrum point linked to dataloggers with a balancing beam attached to the growing tip/plant apex
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.