in today's theodolites laser auto level and theodolites laser liner, the reading out of the horizontal and vertical circles is usually done electronically. the readout is done by a rotary encoder, which can be absolute, e.g. using gray codes, or incremental, using theodolite laser auto level and theodolites laser liner equidistant light and dark radial bands. in the latter case the circles spin rapidly, reducing angle measurement to electronic measurement of time differences. additionally, lately ccd sensors have been added to the focal plane of the telescope allowing both auto-targeting and the automated measurement of residual target offset. all this is implemented in embedded software.
also, many modern laser theodolite and theodolite level, costing up to $10,000 apiece, are equipped with integrated electro-optical distance measuring devices, generally infrared based, 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. this technique laser theodolite and theodolite level is called a resection solution or free station position surveying and is widely used in mapping surveying. the instruments theodolite, "intelligent" level theodolite called self-registering tacheometers or "level theodolite total stations", perform the necessary operations, saving data into internal registering units, or into external data storage devices. typically, ruggedized laptops or pdas are used as data collectors for this purpose.
http://en.wikipedia.org/wiki/theodolite
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