For shorter distances, time-of-flight is not typically used. There's surprisingly little documentation about how these things work online though. From http://

For shorter distances, time-of-flight is not typically used. There's surprisingly little documentation about how these things work online though. From http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939.htm http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939... "The laser diode emits light pulses with a defined wavelength and pulse repetition frequency. Due to the runtime difference between the internal reference path and the external measurement path, the light pulses, reflected on a target and received from the Leica DISTO™, have experienced a phase shift in relation to the light pulses received through the internal reference path. That phase difference between those two signals is proportional to the distance between instrument and target."