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1570s, of unknown origin (see OED for discussion).
An optical instrument used to measure angles in surveying, meteorology, and navigation. In meteorology, it is used to track the motion of a weather balloon by measuring its elevation and azimuth angle. The earliest theodolite consisted of a small mounted telescope that rotated horizontally and vertically; modern versions are sophisticated computerized devices, capable of tracking weather balloons, airplanes, and other moving objects, at distances of up to 20,000 m (65,600 ft).
basic surveying instrument of unknown origin but going back to the 16th-century English mathematician Leonard Digges; it is used to measure horizontal and vertical angles. In its modern form it consists of a telescope mounted to swivel both horizontally and vertically. Leveling is accomplished with the aid of a spirit level; crosshairs in the telescope permit accurate alignment with the object sighted. After the telescope is adjusted precisely, the two accompanying scales, vertical and horizontal, are read