1. When adopted in the field, the guns should seldom be elevated above 3 degrees, as the objects fired at are generally cavalry and infantry, and the lower the angle the longer will the shot preserve its force, and have effect.
2. In the ricochet of a fortification of any kind, the elevation should seldom exceed 10 degrees to throw the shot over the parapet a little higher than the level of the battery; and, on the whole, the best elevation to enfilade a work is from 6 to 9 degrees, measured above the crest of the parapet with corresponding charges.
3. The charge, and elevation being known for any range, when the gun and parapet are on the same level, the same charge, and elevation may be used so long as the difference of level does not exceed one-twentieth of the horizontal distance between them, the elevation being given by the tangent scale, and the gun laid at the parapet, whether above or below its own level.