428 
PRINCIPLES OE GUNNERY. 
Zones of 
fire. 
Probability op Hitting. 
By the Theory of Probabilities it may be shown that the dimensions 
of the zones of fire in which 50 per cent, of the shot would probably 
strike may be obtained by multiplying the mean errors by the factor 
P69. 
If the mean error in range be denoted by R, 
n n lateral error n L, 
a n vertical error n V, 
the depth of the zone containing 50 per cent, of the shot is 1*6912, 
n breadth nun u 1*69 L, 
„ height nun u 1*69 V. 
These zones of fire are quite independent of one another, and are 
bounded by two indefinite parallel straight lines, distant from one 
another by the amount given above. 
CL /I 
D l 
C 
d 
B 
c 
Thus, firing at a horizontal target, if R is the mean error in range, 
then the length included between the two indefinite parallel straight 
lines ab and cd } distant 1*69 R from one another, represents the depth 
of the zone containing 50 per cent, of the shot fired; and if L is the 
mean lateral error, then the length included between the two indefinite 
parallel straight lines ef and gh , distant 1*69 L from one another, repre¬ 
sents the breadth of the zone containing 50 per cent, of the shot fired. 
