A thedolite is an instrument used to measure horizontal and vertical distances using lenses and lines. They include several components, such as a telescope, a leveling mechanism, a tripod and a compass. Theodolites are used for surveying and construction to obtain precise readings of landforms so construction projects remain level and plumb with the ground.
Contemporary surveyors use electronic digital theodolites in their work. The telescope of a theodolite allows the user to view the target object easily. An adjustable tripod lets the mechanism stand on uneven ground. A leveling mechanism allows users to take accurate angle measurements. A compass or GPS system measures precise locations on construction sites.
Old theodolites are mounted on A-frames with leveling plates and a weighted plumb bob. The A-frame lets the telescope tilt up and down. Leveling plates keep the device from tilting. A plumb bob measures possible discrepancies on the ground upon which the tripod rests. Any deviation from being level and plumb means bad data.
There are four basic types of modern theodolites. Repeating theodolites take accurate horizontal readings by averaging results. Directional theodolites do not move like repeating models; they let users take measurements by subtracting two readings. Electronic digital theodolites automatically measure horizontal and vertical angles, thereby reducing mistakes taken from manual measurements. A total station adds in automatic distance measurements from a single setup.