56 A CALCULATION OF PROBABILITY OF FIRE. 
The steps necessary to calculate the percentage of effective shots one 
may expect at a moving objective are 
(1) to reduce the objective to an equivalent horizontal area or 
target having a certain length and breadth, which will vary with (a) the 
gun, (6) the height of the gun above the sea, (c) the range, (d) the 
dimensions of the objective, and (e) its path ; 
ay 
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(2) to calculate the modifications necessary in the dimensions of 
the 50 per cent. zones when firimg under ordinary conditions at a 
moving objective ; 
(3) to compare these dimensions with those of the target. 
