[f. Gr. τάχος speed + -METER: cf. barometer.] a. An instrument by which the velocity of machines is measured. b. An instrument for measuring the velocity of a moving body of water, a current-measurer.
1810. Donkin, in Trans. Soc. Arts, XXVIII. 185. An instrument of my invention for indicating the velocity of machines, and which may not improperly be called a Tachometer.
1825. J. Nicholson, Operat. Mechanic, 42. The method of putting the tachometer in motion whenever we wish to examine the velocity of the machine.
1864. Webster, Tachometer,… (b.) an instrument for measuring the velocity of running water in rivers, canals, &c.
1875. L. D’A. Jackson, Hydraulic Man., I. 84. The tachometer of Brünings is the best instrument of this type.
So Tachometry, the scientific use of a tachometer; the measurement of velocity.
1891. in Cent. Dict.
