Tacheometer is a Theodolite designed for rapid surveying measurements. Tacheometer is also called as Tachymeter. Tacheometer is an Electronic Theodolite that is used for rapid measurements and determines, electronically or electro-optically, the distance to target, and is highly automated in its operations. Tachymetry or tacheometry is the process of measuring distance indirectly. This can be done by measuring time and speed in a moving vehicle or by sighting through small angle a distant scale transverse to the line of sight.
Tacheometry is a branch of surveying in which horizontal and vertical distances are determined by angular observations with a tacheometer. There is no linear measurement. Tacheometry is not as accurate as chaining,but it is more rapid in rough and difficult countries where leveling is tedious and chaining is inaccurate and slow.
Tacheometric surveying used for preparing contour plans, hydrographic surveys, locations surveys of roads, railways etc. Instruments used in tacheometric survey are tacheometer, stadia rod, pegs, ranging rod, offset rods, etc.
Tachymeter scale is also used as the name of the scale sometimes inscribed around the rim of an analog watch, useful in converting time intervals to speed or other rates of events. Tacheometry in surveying include the use of stadia rods with theodolites or plane-table alidades. Another device used in tacheometry is the subtense bar.