It is usually an integrated unit called EDMI (Electronic distance - measuring instrument) consisting of an electro-wave generator, an oscillator, a modulator, a transmitter, and a receiver etc. The type, range and accuracy of an EDM instrument depend on the type of carrier waves it can generate and subsequently can transmit, receive and analyze (Table 10.1).
An EDM instrument generally gets mounted in the framework of an electronic theodolite. The net result is a single instrument termed as total station (Figure 10.1) which can be used to measure all the fundamental measurements involved in surveying.