(ii) Objective.—The point at which the fire is directed may be the actual objective, or ground in its vicinity which is more suited to observation of the strike of the bullets.
(iii) Position for Observation.—The best position from which to observe fire is behind, and, if possible, above the firers; but in this position the bullets which fall short will be most easily seen, and may be mistaken for the nucleus of the fire. Further, all shots will appear to strike nearer to the observer than is really the case.
(iv) Hints for Observers.—To an observer on or behind a flank of the firers, shots which pass over the mark will appear to fall towards the flank on which he is posted, and those which drop short to fall towards the opposite flank. Thus, if the majority of shots seem to an observer on the right flank to fall to the right of the mark, the range has been over-estimated, and if they seem to fall to the left, it has been under-estimated.
4. Verifying Ranges by Fire.—When there is time and opportunity for doing so, ranges which have been taken beforehand, especially those taken in preparing a defensive position, should be verified by the results of firing a number of rounds.
Section 39.—Ranging by Auxiliary Methods and by Instruments.
1. Training in ranging should include instruction in practical auxiliary methods such as by maps and range-finding instruments. Exercises in ranging by means of maps, range-finders, and the eye, used in combination, should form an essential part of the fire-direction practices of the annual course of musketry.
2. Ranging by Map-Reading.—Ranges may be ascertained by the use of small scale maps, though large scale maps, if available, will be better for this purpose. Instruction in field-sketching and reconnaissance affords excellent opportunities for training in judging distance. For map-reading, see Signalling of this series; and for field-sketching and reconnaissance, see Drill and Field Training of this series.
3. Back-Reckoning.—Back-reckoning may be defined as deduction as to distance made from any known range. For instance, in advancing on a position the range of which is ascertained on commencing the advance, the distance gained by each forward movement may be deducted from the original range of the position in estimating its range for firing on it at successive halts. Again, the range of an objective further away than another objective, of which the range is known, may be estimated by adding to the known range the estimated distance of the former from the latter objective. An example of back-reckoning is shown in [Fig. 44].
4. Ranging by Gun-Flash and Sound.—Light travels at the rate of 186,000 miles a second, so that a gun-flash is practically seen as it issues from the muzzle, irrespective of the distance of the observer. Sound, on the other hand, travels about 1,100 feet, or about 365 yards, a second. By timing the interval between seeing the flash of a gun and hearing the report, its approximate distance may therefore be deduced. This, of course, will only be possible when the position of the gun is betrayed by the flash, and when guns are fired singly at appreciable intervals, or simultaneously, so that there is practically one flash and one report at a time.
5. Range-Finding Instruments.—A certain number of officers, N.C.O.’s, and men in each unit will be trained to use the One-Man Range-Finder or the Mekometer instrument, full directions regarding the use of which will be found in the official handbooks dealing with these instruments.