The facility for long distance measurements consists in a 28 m long rail fixed to a series of pillars which rest directly on the ground released from the vibrations of floor and wall. The measuring system is based on a heterodyne interferometer, whose mobile arm consists of a hollow retro-reflector mounted on a structure that can run along the rail, so-called "carriage".

The system can operate in two modes: a first mode, based on fringe counting for low values of carriage speed and with uncertainty in the order of 0.2 μm at maximum distance; a second mode, based on the Doppler effect and suitable for high values of carriage speed with uncertainty in the order of 1.5 μm at maximum distance.

The system can be used both for the calibration of commercial laser distance meters and for the calibration or characterisation of absolute rangefinders and interferometers.