Use of the 
rule. 
206 SLIDE RULES FOR BATTERY COMMANDER'S CORRECTIONS. 
when using Case II. for laying we have to allow for travel at 
1000 yards 54 seconds 
15007 Fy Oe), 
2.00 On (ee, and so on. 
Therefore under 54 seconds make a mark at the lower edge and 
number it 1000, another under 64 numbered 1500 and so on. 
To use the rule bring the division on the scale of seconds, which 
corresponds with the number of seconds during which the range alters 
by 50 yards, under the black arrow, then under the range will be found 
the required correction. 
For example, supposing the range to be increasing by 50 yards every 
7% seconds and the range to the target to be 3500 yards. Bring 7} 
on the scale of seconds under the black arrow, and under 3500 on the 
scale of ranges, we find 84 which is the correction required. 
When using Case I. for laying the “ time of firing” will be different 
to that for Case IJ.; the slide is therefore made reversible so that the 
scale for Case I. can be placed on one side and that for Case IT. on the 
other. 
