This is copied from the 1863 Hvy Art. manual. Thought you might find this of interest. It explains the use of the stakes, plumb's levels ect.
Many of the N-ssa crews follow some variation of this method.
Pointing Mortars
As mortars are usually masked from the object to be bombarded by an epaulment or parapet, different means from those which are used with guns and howitzers become necessary for giving them their direction.
There are several means proposed, all of which, however, are reduced to determining practically two fixed points which shall be in line with the piece and the object, and
Sufficiently near to be readily distinguished by the eye. These points being covered by the plummet, determine a vertical plane, which, when including the line of metal, (?) becomes the plane of fire.
Premising that the mortar is so laid that its axis will be nearly in the plane of fire, and that the line of metal is ascertained by the gunners level and marked with chalk, best manner of directing the mortar is by means of pointing-stakes.
This method uses point-stakes to establish one of the fixed points upon the parapet, and another in the rear of the piece. Then by a cord, called the pointing-cord, stretched between these two points, with the plummet suspended from it, a vertical plane is determined with which the line of metal is made to coincide.
To fix the points, a stake, a foot or more in length, is driven firmly into the crest of the epaulment as nearly as practicable in the vertical plane passing through the axis of the platform; sighting by this stake, another long one is planted three or four feet in front of it In line with the object. To this stake the cord is temporarily attached, and stretched by the first stake, just grazing it to a point one yard in the rear of the platform. At this point a third stake is driven. The pointing board (this is a piece of wood one foot long, two or three inches wide, and one inch thick, having a notch cut in the middle of one side to fit on the stake, which is graduated into equal divisions from its middle. It serves to wind the pointing cord on when not in use.) is laid on the ground at the foot of the stake. The cord is removed from the second stake, which now may be taken away, and permanently attached to the first.
To direct the mortar, the cord is stretched to the top of the stake by the left hand, while the plummet is suspended against it by the right, or, the plummet maybe attached to the cord in the rear of the mortar.
It is evident that when the cord, the plummet, and the line of metal are in one plane, the mortar is properly directed.
In case the shell should, nevertheless, strike constantly to the right or left of the object, the pointing-cord is shifted to some notch on the pointing board to the right or left, until the shell falls at the desired point.
