Both theodolites and transits are instruments used by surveyors to measure horizontal and vertical angles, measure distances and determine elevations. Transits have an open design and are read through a scale on metal rings. Theodolites have a closed design, are lighter than transits and are read through a scale on glass discs. In general, theodolites are more precise than transits.
Traditionally, transits have been the preferred device for American surveyors for taking measurements. Transits have one primary advantage over theodolites. The telescope part of the device flips all the way over for easily backtracking and doubling measurements during surveying work. The word "transit" comes from this specific capability of the instrument. Another acceptable name for the transit is the "transiting theodolite" or the "transit theodolite."
Electronic digital theodolites are the preferred surveying measurement device for surveyors worldwide. Electronic theodolites work quickly and eliminate human error from misreading scales. Infrared measuring devices work in conjunction with complex software to minimize errors and provide accurate results. These electronic theodolites also record and save the surveying data to eliminate the need for paper and pencil or audio recording devices in the field. The data is later transferred to computers, where complementary software analyzes it for map-making or other surveying use.