425 
PRINCIPLES OE GUNNERY. 
RIFLED ORDNANCE. 
BY 
CAPTAIN J. SLADEN, R.A. 
PBOEESSOB OE ABTILLEBY, B.M. ACADEMY, WOOLWICH. 
(Continued from p. 368.) 
CHAPTER VIII. 
Accuracy and Probability or Fire. 
Mean Range.—Mean Lateral Deviation.—Mean Vertical Deviation.—Mean Error in Range, or 
Mean Longitudinal Error.—Mean Lateral Error.—Mean Vertical Error.—Mean Absolute 
Error.—Method of Estimating the Accuracy of Small-Arms and Ordnance.—Example of 
Testing Guns for Range and Accuracy.—Zones of Eire.—Probable Rectangles.—Table of Pro¬ 
bability Factors.—The Probability of Hitting a Target of given Dimensions.—Causes which 
Affect Accuracy of Fire.—Variations in Muzzle Velocity.—Unsteadiness of the Projectile as 
it leaves the Bore and during Flight.—Wind.—Personal Error in Laying.—Inclination of 
the Trunnions to the Horizon.—Unsteadiness of Gun, Carriage, and Platform on Firing. 
In order to judge of the relative accuracy of fire of different guns, it 
is necessary to fire a large number of rounds from each gun, and 
compare the results. It is usually done by firing at a horizontal 
target, and if possible at a vertical target. 
The mean range is obtained by dividing the sum of the ranges of Mean 
range. 
z l " 
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