AUTO-SIGHTINGK 
129 
Colonel Watkin has given figures showing the effect in the case of 
a 6-in. gun of tilting the racer path “ 4' down to the point,” the 
assumed height of the gun being fifty feet. In this case at 4,000 
yards, the range-finding angle—that is the angle of depression of the 
line of sight—is 14*'3. Deducting 4', we have a range-finding angle 
corresponding to 5,564 yards, and at 5,564 yards 4' will shorten the 
range by thirty-two yards. The range obtained, in these conditions, 
will therefore be 5,532 yards, involving an error of 5,532 — 4,000 
yards = + 1,532 yards. 
The tilting of the racer path is, however, much more likely to be in 
the other direction, or down to the rear because the effect of recoil 
creates this tendency. If 4' is added to the range-finding angle of 
14*3', the corresponding range is 3,131 yards. Adding forty-five 
yards due to the increase of 4', the range becomes 3,176 and the error 
is 3,176 — 4,000 yards = — 824 yards. Such an error is of course 
inadmissible; but it differs materially from 1,532 yards and might, 
therefore, have received mention in an analysis of the situation. It 
should also be noticed that the error tends to diminish rapidly as the 
range-finding angle approximates to the angle of descent. 
While an inspection of Colonel Watkin*s table would naturally lead 
to the conclusion that an inclination of 4' would render the use of an 
auto-sight impossible, the actual facts differ materially. I am inclined 
to think that the auto-sight has been regarded as a range-finder and 
criticised from this point of view. This is clearly a misconception. 
A range-finder is an instrument for finding and accurately recording 
ranges. It does not concern itself with the shooting of the gun 
and such matters. On the other hand, the auto-sight is a device 
enabling a range-finder to be dispensed with. It has nothing to do 
with the recording of ranges and it must take account of conditions 
which the range-finder ignores. 
No gun shoots exactly to its range table and for various reasons 
there arises what is conveniently if vaguely called the “ error of the 
day.** Theory lends us no assistance in eliminating this error, and we 
have to fall back upon the method employed by our ancestors long 
before sights or range-finders were in existence. In other words, we 
must observe the fall of the projectile, estimate the error of range and 
correct accordingly. The auto-sight provides the means of correcting 
in accordance with such an observation, and evidently errors due to 
inclination of the racer path are included in the correction. 
For example, if with a 6-inch Q.F. gun at a height of fifty feet 
standing on a racer path inclined 4' forwards, the correction can be 
made from an observation at 4,000 yards, the errors going up the 
range are :— 
Range. Errors in range. 
1,000 — 32 yards. 
2,000 —J|37 „ 
3,000 -*25 
4,000 0 
