A theodolite is a type of telescope that can be used on both horizontal and vertical planes to measure angles. Theodolites are most commonly used by surveyors during construction projects. The instrument is operated by placing the telescope at one point, aiming the piece at the second measuring point, and then reading the measurement through the eye piece.
Place the theodolite at the starting point for the measurement. The location of the instrument marks the first point in the angle you want to measure.
Adjust the height of the theodolite so that you can comfortably see through the eyepiece. Use the adjustment knobs on the instrument to fine tune the height, lateral movement and focus.
Make sure the theodolite is sitting perfectly level by adjusting the plummet. This piece will be located underneath the telescope, on the bottom of the instrument.
Look through the eyepiece, moving it up or down to adjust the angle of the measurement. A red line will highlight the areas that are currently being measured. Both horizontal and vertical measurements will appear on the side of the instrument's viewing scope.
Theodolites are highly sensitive, and should be handled with care. The slightest damage from improper handling of the instrument can alter the readings and compromise their accuracy.