tachymeter (tacheometer, tachometer, tacheographometer)-¹ A 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 integral part of the instrument. ² An instrument in which the base line for distance determinations is an integral part of the instrument; tachymeter. Range finders with self-contained bases belong to this class of instrument, but they do not usually afford the means for determining elevation. ³ An instrument equipped with stadia wires or gradienter, the base for distance determination being a graduated rod held at the distant point.

tachymetry, tacheometry—Surveying method used to obtain horizontal distances and differences in elevation by indirect methods, which are based on the optical geometry of the instruments employed. Sometimes referred to as “optical distance measurement,” “telemetry,” or “stadia.” Among the instruments used in tachymetry are the engineer’s transit or telescopic alidade with a level rod or stadia rod, theodolite with a subtense bar, self-reducing theodolite with a level rod, distance wedge with a horizontal distance-rod, reduction tacheometer with a horizontal distance-rod, and rangefinder.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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