(iv) A General Rule.—A good general rule to remember for practical purposes is that when a target is indistinct distance is apt to be over-estimated, and that when a target is distinct distance is apt to be under-estimated. This general rule roughly sums up the effects and the various factors mentioned in paras. (ii) and (iii), which respectively tend to render targets less or more distinct.
3. Judging Lateral Distance by Eye.—The following is a rough guide for judging lateral distances running at right angles to the observer at various distances. With one eye shut and the hand at arm’s length to the front with the fingers perpendicular, the breadth of six fingers will cover 100 yards of lateral distance at a distance of 500 yards from the observer. Under the same conditions, the breadth of three fingers will cover a lateral distance of 100 yards at a distance of 1,000 yards. The breadth of two fingers will cover a lateral distance of 100 yards at 1,500 yards, and the width of the thumb will roughly cover 100 yards of lateral distance 2,000 yards away. This method may be employed for estimating the approximate length of an enemy’s column, or the extent of frontage known to be occupied by him.
4. Method of Instruction—(i) Units of Distance.—All the methods mentioned in para. 1 should be practised by officers, N.C.O.’s, and men under a variety of practical conditions, and in the prone, kneeling, and standing positions, until it is found that distances can be judged approximately from the general impression conveyed to the eye. The class will first be familiarized with short units of distance not exceeding 600 yards. Special care will be taken to enable soldiers to recognize the distance of 600 yards, as it is the limit of individual fire.
(ii) Figures.—The class will at the same time study the visibility of the figure standing, kneeling, and lying at known distances. They will be required to remember the results of their observation, and be given opportunities of seeing figures in varying conditions of light, atmosphere, and background at known distances.
(iii) Features of Ground.—The class will next be practised in judging the distance of natural features of ground, such as folds of ground, hedges, patches of undergrowth, and other forms of cover, at various known distances. This instruction will be followed by judging the distances of fatigue-men seen at unknown distances in the different firing positions both in the open against various backgrounds and partly behind cover. The class will then be practised in judging the distance of features of ground and different forms of cover at various unknown distances. These various practices should be carried out with the class in the standing, kneeling, and prone positions.
(iv) Reasons for Estimates.—Each observer should be asked by the instructor to give reasons for his estimate of distance to guard against the habit of rough guessing. To train observers in the habit of taking into account every factor which will help them to judge distance, the instructor should consider and explain the effects of local conditions and other factors which affect judging the distance of each object he indicates after the class have made their estimates. Ample time should at first be allowed for judging distance, but as progress is made the time should be limited. The above exercises must include instruction in estimating lateral distances. Rough guessing is never to be allowed.
5. Aids to Judging Distance by Eye.—(i) The class should be trained in various methods of assisting the eye when the distance of objects is especially difficult to estimate approximately. For example, a maximum and minimum estimate of the distance may be made, and the mean taken as correct. Half the distance from the object may be estimated with the aid, if possible, of some feature of ground, and double may be taken as correct. When the object is partly hidden in a fold of ground, or when it is of unknown size, distance from it may be estimated with the help of some object of known size, such as a natural feature of the ground or a human figure which may be near it.
(ii) Other rough methods which will assist them in judging distance approximately may be explained to the men. For instance, the foresight of the rifle when correctly aligned will be approximately equal to the height of a standing figure at 400 yards. The width of an ordinary pencil held horizontally at arm’s length before the eye will cover an upright figure at 200 yards, and the lead at its thick part will cover a standing figure at 600 yards.
6. Tests in Judging Distance by Eye—(i) Directions regarding Tests.—In every company, and at depôts, in addition to instructional exercises, at least one test in judging the distances of four objects will be held for all ranks in every three months, the distances of the objects being between 200 and 800 yards.
All company officers, non-commissioned officers, and those men who are in possession of badges for judging distance, will also be tested once in every three months under regimental arrangements in judging the distances of four objects between 200 and 1,400 yards.