210 
FIELD ARTILLERY FIRE. 
of the piece, i.e., the breadth of the probable rectangle. For this reason 
it is not necessary to correct the deflection after a single round, unless 
the deviation observed exceeds the breadth of the probable rectangle. 
If it is less than this amount the mean of several rounds must be taken 
as a basis for correction. 
The deflection for each gun varying according to the position of the 
wheels (except when Scott’s sights are used), the proper correction 
must be made for each by the gun-layer and the Sectional Officer is 
responsible that it is made. In the case of a strong side wind the 
correction will apply to all and will be ordered by the Battery Com¬ 
mander. When Scott’s sights are used this deflection given by the 
C.O. for wind should include that necessary to compensate for drift. 
As observations for lateral corrections can best be made from a 
position near the gun itself, these corrections are the business of the 
Sectional Officers. 
Mental calculations are very little to be relied upon in the field and 
it will be found better, instead of calculating out a correction for deflec¬ 
tion to make a bold alteration which will probably bring the projectile 
to the other side of the target and then split the difference, in fact to 
apply the bracket system, which has always been found quicker than 
any creeping up. 
Amount of assistance to be got from the Range-Finder in ranging. The 
advantage of the range-finder is that the great errors that arise in 
judging distance are eliminated, and we may therefore hope that the 
elevation as given by range-finder will place our first round somewhere 
close to the target. But, owing to the variable factors influencing the 
trajectory, mentioned in the beginning of this chapter, it would not do 
to accept this elevation without verification. A verifying series might 
be fired at once at the elevation so given, but this might lead to loss of 
time and to creeping up to the target, it is better therefore to attempt 
at once to find the small bracket, or at long ranges a bracket of 100 to 
200 yards, by this means the process of ranging is considerably short¬ 
ened. 'Thus, if the range-finder gives 2710 yards : 
1st round, elevation 2700 yards short. 
2nd „ „ 2750 „ „ 
3rd „ „ 2800 ,, over. 
Let us assume that the range is verified to be 2775 yards, that is to 
say that in order to make a shell travel a measured distance of 2710 
yards it is necessary to put up elevation for 2775 yards, this difference 
of 65 yards is known as THE ERROR OF THE DAY and will vary 
according to atmospheric conditions, state of powder, &c. 
The value of knowing the error of the day is this, that, at the second 
or later series, the knowledge can be made use of in shortening the 
process of ranging. Thus, suppose the next range as given by range¬ 
finder is 2325 yards, the error of the day is known to be 65 yards, the 
elevation for that range will therefore be 2390 yards. 
1st round 2400 yards over. 
2nd „ 2350 ,, short. 
It would not be safe to omit bracketting the target because the 
range-takers might have made a mistake. 
