Instead of stop watches, therefore, we used a timing device capable of recording the most minute time-intervals with perfect precision.

The whole system was immeasurably superior to the German, and at least twenty times as accurate, for the British system was absolutely automatic.

It recorded the arrival of the sound at the various microphones instantaneously on a permanent record; while the German system, apart from its crude method of measuring time, was subject to the combined errors of four human 'microphones.' The British system requires only one forward observer, placed well ahead of the base, and all he has to do is to press a button and start the apparatus before the sound reaches the microphones.
"The photographic record is ready for the computer in from six to ten seconds, and the gun position can be found and plotted in three or four minutes.
"Sound ranging also can be used for ranging our own guns with great accuracy.

When a record has been obtained of a hostile gun, all that need be done is to record the burst of our own shell and give corrections to our battery until the record of our shell-burst is identical with that of the hostile gun.

The shell must then be on the target.
"The system works equally well by day or by night, in rain or in fog.
Its one enemy is a wind which blows towards the hostile gun and prevents the sound reaching the recording apparatus.