The observation of fire is essentially the following operation, repeated for each shot or salvo: Locating on the ground the position of one point, which is the point of burst, and announcing its situation in reference to another point, which is the target.
But it has been demonstrated that it is impossible, without using the map, to determine the error in range of one point relatively to another point not on the same alignment.
The operation must consist in:
1. Spotting on the map the point of burst.
2. Reading its position in reference to the target.
The observation of the burst—that is, the spotting of the point of impact—is the same whether the observation is direct or lateral.
1. PREPARATION OF THE FIRE.
Draw on the map, and copy if possible on a vertical photograph, the line balloon target (alignment of the center of the objective) and draw through this point a perpendicular to the alignment. In case the observation is lateral, draw also the line battery target and its perpendicular.
To draw the line balloon target, it is not necessary to know the horizontal projection of the balloon. It is enough to find on the ground a point situated directly on the alignment of the center of the objective.