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A crescograph is a device for measuring growth in plants. It was invented in the early 20th century by Sir Jagadish Chandra Bose.
The Bose crescograph uses a series of clockwork gears and a smoked glass plate to record the movement of the tip of a plant (or its roots) at magnifications of up to 10,000. Marks are made on the plate at intervals of a few seconds, demonstrating how the rate of growth varies under varying stimuli. Bose experimented with temperature, chemicals, gases, and electricity.
The Electronic Crescograph plant movement detector is capable of measurements as small as 1/1,000,000 of an inch. However, its normal operating range is from 1/1000 to 1/10,000 of an inch. The component which actually measures the movement is a differential transformer. Its movable core is hinged between two points. A micrometer is used to adjust and calibrate the system. It could record plant growth, magnifying a small movement as much as 10,000,000 times.