Page:Machine-gun tactics (IA machineguntactic00appl).pdf/65

 pocket clinometer or other mechanical means; or, if heights can be obtained from a contoured map, from the formula:

m = (h 1146)/R

where h = difference in feet of height between guns and target; R = range in yards.

(2) When target is not visible from immediate vicinity of guns, m may be found from the following formula:

(a_{1} × GO + a_{2} × OT)/GT

Where a_{1} is the angle of sight from G to O; a_{2} is the angle of sight from O to T.

Angles of elevation are read plus, angles of depression minus; T being the target, G the gun, and O the observer.

Before firing it is necessary to ascertain that the trajectory will clear the intervening crest—i.e. see that the angle of slope to the top of crest is less than the angle of Q.E. at which the gun is likely to be fired. If there is an obstacle some distance in front of the guns, to ascertain if the