EDM instruments can be classified in terms of their range.

Short range instruments have a range of up to 2000m with a single prism. They are usually equipped with an infrared or laser diode to generate the carrier wave. Typically their accuracy is about ±(5mm + 5ppm).

Long range instruments require a greater power output than short range instruments. This can be achieved using higher grade diodes, Xenon flash tubes or HeNe gas lasers to generate the carrier wave. Typically their accuracy is about ±(5mm + 2ppm).

Some instruments have high precision capabilities, for example:

Precision distance meters: ~ ±(1mm + 2ppm)
High precision distance meters: ~ ±(0.2mm + 0.2ppm)

± (A mm + B ppm)

This is considered as a standard deviation at the 66% confidence level.

The term A is determined by such factors as the phase resolution of the EDM, short periodic errors present in the instrument and the accuracy of any present constants (such as the reflector constant).

The term B is predominantly determined by frequency drift of the oscillator under field conditions due to temperature changes. Precise EDM instruments usually have some type of temperature controlled or compensated oscillator to achieve the low ppm term. With longer distances the ppm term becomes more significant.