(a) The soldier may decide that the object cannot be more than a certain distance away nor less than a certain distance; his estimates must be kept within the closest possible limits and the mean of the two taken as the range.
(b) The soldier selects a point which he considers the middle point of the whole distance, estimates this half distance and doubles it, or he similarly divides the distance into a certain number of lengths which are familiar to him.
(c) The soldier estimates the distance along a parallel line, as a road on one side, having on it well-defined objects.
(d) The soldier takes the mean of several estimates made by different persons. This method is not applicable to instruction.
[1395]. Determination of distance by trial shots or volleys. If the ground is so dry or dusty that the fall of the bullets is visible to the naked eye or through a field glass, distance may be determined by using a number of trial shots or volleys.
In the case of individual trial shots, the soldier sets his sight at the estimated range, watching to see where the bullet strikes,—or some other man, with or without field glasses, may watch to see where it strikes. If the bullet strikes beyond the target, the estimated sight setting is decreased; if it falls short, the sight setting is increased.
In case of volleys, the sights are set at the estimated range and a volley is fired. If it appears to strike a little short of the mark, an increase in elevation of 100 yards is used for the next volley. When we have the target inclosed between two volleys, we take the mean of the estimated ranges for the correct range. For example, if the first estimated range were 1000 and the second 1100, the correct range would be 1050.
[1396]. Appearance of objects: How modified by varying conditions of light; difference of level, etc. During instruction the men should be taught the effect of varying conditions of light and terrain upon the apparent distance of an object.
Objects seem nearer—
(a) When the object is in a bright light.