Construction of theodolite

The theodolite consists of a telescope pivoted around horizontal and vertical axes so that it can measure both horizontal and vertical angles.

Today's theodolites are usually equipped with integrated electro-optical distance measuring devices, allowing the measurement in one go of complete three-dimensional vectors -- albeit in instrument-defined polar co-ordinates -- which can then be transformed to a pre-existing co-ordinate system in the area by means of a sufficient number of control points.

The upper plate PP is bored centrally to receive a parallel or conical pillar which supports the lower circle of the theodolite or the arm of the level which carries the telescope.

In the theodolite the edge of the piate is beveled and divided into 360 or 400 degrees, and to half degrees, or to 20 minutes or 10 minutes, according to the size of the instrument.

Surveying Instructions with NBMG's EDM Theodolite
Level the theodolite by first adjusting the knurled leveling screw wheels so bull's-eye level is centered.
Extend rod so prism center is within 1 cm of its objective height, with rod end resting on ground and in vertical orientation (check bull's-eye level on rod).
At the theodolite, the surveyor sights on the prism, first with the sight atop the telescope, then through the telescope.

Different definitions of theodolite
An optical instrument consisting of a small mounted telescope rotatable in horizontal and vertical planes, used to measure angles in surveying, meteorology, and navigation.
The theodolite hit a jutting cliff-ledge and exploded like a shell; the books, inkstands, paint-boxes, compasses, and rulers showed for a few seconds like a swarm of bees.

A theodolite is mounted on a tripod by means of a forced centering plate or tribrach, containing three thumbscrews for rapid leveling.

THEODOLITE calibrated optical instrument used to determine relative position in surveying, navigation, and meteorology.
It is similar in construction to a surveyor's transit, consisting of a telescope fitted with a spirit level and mounted on a tripod so that it is free to rotate about its vertical and horizontal axes.

Though for sketch maps the compass or graphic techniques are acceptable for measuring angles, only the theodolite can assure the accuracy required in the framework needed for precise mapping.