FIELD ARTILLERY FIRE. 
209 
on graze are obtained and then shorten the fuze by one-quarter or one- 
half. By this means the burst of the shell within an effective distance 
of the target is ensured. 
Error of burning of the Fuze. Taking the result of many rounds 
fired at battery service practice by a well-trained battery, it has been 
found that with the small time and percussion fuze the mean error of 
burning is about f9 yards. This of course takes into account not only 
the variable burning of the fuze but also a certain amount of indifferent 
setting of the fuzes, which after all is a service condition. 
It will be seen therefore that if it is desired to get a mean point of 
burst within about 100 yards of a target that a certain proportion of 
the shell will burst on graze. 
Fuze scale. The fuze scale is merely approximate and is compiled 
for the burning of the fuzes at the sea level. The higher the altitude 
the slower burn the fuzes on account of the diminished supply of 
oxygen and the diminished pressure of the air. Buies are given in the 
drill-books for calculating this increase in the length of burning but 
calculations of this sort are little to be trusted in the field and all in¬ 
formation required may be got from the first pair of trial fuzes if they 
be set sufficiently short to burst in the air and not on graze. 
To find the correct length of fuze. In this portion of the process of 
ranging the same general rule applies as in the former portion, viz., 
that a creeping style should be avoided as leading to a waste of time 
and ammunition. 
Alterations should be bold, that is, of not less than *5, with a metal 
time fuze. If the correction is bold then the target is soon bracketted 
between two lengths of fuze, one too long and the other too short; the 
amount short may be seen by observation and the difference between 
the two lengths split in the proper proportion to give the correct height 
of burst. 
It is when shell burst on graze that the boldest alterations are 
necessary, and at long ranges one or two whole divisions is a permissible 
alteration, because it is impossible to tell how much too long the fuze 
is. As an example, an officer firing at a range of about 3800 yards 
and using the middle time fuze, gave the first pair of fuzes 25, these 
burst on graze, he then came back ’5 at a time firing two fuzes at each 
length, until he got to 21*5 which was the correct length. He thus 
took 16 shell before he arrived at the right length, which then had to 
be verified. If he had made a bolder alteration he would probably 
have found the correct length in 6 or 8 rounds. 
In ranging for length of fuze, or afterwards, alterations should never 
be made on the result of the observation of one round. Trial fuzes 
should always be fired by sections and the mean of two bursts taken as 
the basis for corrections. 
Corrections for deflection. In order to facilitate observation it is im¬ 
portant that the guns during ranging should be carefully laid for 
direction and it is the duty of the sectional officers to assist the Bat¬ 
tery Commander by attending to this. 
A lateral deviation is not always caused by the wrong setting of the 
deflection leaf, it may sometimes be the result of the natural dispersion 
