A theodolite is a surveying instrument used to measure angles between differen t points accurately, enabling them to be plotted in three dimensions. A sighting telescope is used to locate measuring points on suveying poles; to align the telescope it is rotated about a horizontal or vertical axis. The precise angles of rotation in these planes are measured by using a micrometric microscope to read a scale on glass protractors. Modern computerized theodolites takes these measurements electronically, and use lasers to measure distance.

The theodolite represents a development of the transit, which traditionally included only the horizontal scale.