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AUTO-SIGHTS. 
POSSIBLE ERRORS DUE TO NON-VERTICALITY OF PIVOT. 
BY 
MAJOR M. O. HOPKINS, R.A. 
E ECENTLY I had occasion to calculate to what extent the range 
would be affected by want of level in the base-plate in the case 
of Q.F. guns fitted with automatic sights. And one of the guns for 
which I worked this out was a 6" Q.F. at a height of 50 feet with a 
muzzle velocity of 1,882 f.s 
Calculating to the nearest yard, I found that in this case the errors 
in range which would arise from a want of level of 4/ in the base-plate 
would be those shown in the following tabular statement: — 
Error. 
Range. 
Mounting Depressed. 
Mounting Eli 
jooo 
+33 yards 
— 31 yards. 
2000 
+ 278 yards 
— 200 yards. 
3000 
+ 752 yards 
— 474 yards. 
4000 
+ 1512 yards 
-833 yards. 
T hese figures differ very much from those given by Colonel H. S. S. 
Watkin, C.B., in the R.A.I. “ Proceedings ” of last June, and in a less 
degree, those for 4,000 yards, from the results arrived at by Colonel Sir 
G. S. Clarke, K.C.M.G. which were published in the “ Proceedings ” for 
March of this year. 
Whether my calculations are correct or not, I venture to publish them 
as a step towards the solution of a problem which is of the greatest im¬ 
portance to all Garrison gunners. For, however truly base-plates and 
roller paths may be laid, they cannot always remain level; and there 
can be no doubt that a trifling want of level in them will cause great 
errors in range. 
The required corrections for these errors cannot be put into the cor¬ 
rection for the error of the day, since they will vary with the line of 
fire. In the majority of cases a Q.F. gun would have to follow the 
enemy’s vessel through a large arc of fire. Such an arc might extend 
to 180 0 , and if the gun were a 6 " Q.F. at the height of 50 feet and there 
happened to be an initial want of level of 4' when the first round was 
fired at a range of 4,000 yards, the last round being fired at the same 
range as the vessel passed out of arc, the corrections would vary with 
the range and training between + 1,512 and — 833, always supposing 
that my theory and calculations are correct. 
9. VOL XXVI. 
