An auxanometer is an apparatus for measuring increase or rate of growth in plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s.

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

Magnitude

Magnitude Is A Part Of An EarthquakesMagnitude may refer to:In mathematics:*Magnitude , the relative size of a mathematical object*Magnitude , a term for the size or length of a vector...

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 the laboratory, the field, and the classroom.