Tachymeter

n. device that measures the revolutions per minute of a revolving shaft

A tachymeter (also tachymetre or tacheometer) is a kind of theodolite used for rapid measurements and determines, electronically or electro-optically, the distance to target, and is highly automated in its operations. Tachymeters are often used in surveying.
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Noun
1. a theodolite designed for rapid measurements
(synonym) tacheometer
(hypernym) theodolite, transit

n. tachymeter, instrument for measuring speed or for measuring rotations per minute

Surveying instrument designed for use in the rapid determination of distance, direction, and difference of elevation from a single observation, using a short base which may be an intergraph part of the instrument.