Laser range finder

In a laser rangefinder which transmits laser pulses and receives them after reflection, range being determined from the pulses' time of flight, delays lines 411, 413 ensure that internal delays are compensated for so that the difference in time between the outputs of delays 411, 413 equals exactly the time of flight of the pulses. This time is determined by further delaying 412 the delayed transmitted pulse until the further delayed transmitted pulse coincides with the delayed reclined pulse; the further delay then corresponds to the time of flight. Searching for coincidence may be facilitated by arranging for the delayed received pulse to be lengthened initially by delay 413, and then coarse coincidence is established, shortening it.