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A. M. BATEMAN MILITARY AND GEOLOGIC MAPPING 



It is 9 inches long, % of an inch wide, and 3/16 of an inch thick, with 

 two-inch arms at either end. This height of arm gives an accurate sight 

 through a vertical angle of about 12 degrees, and by extending the line 

 of sight upward from the slots a sight almost as accurate may be obtained 

 through twice that vertical angle. The slots are about 1/30 of an inch 

 wide, giving a fine line of sight. One side of the alidade should be left 

 rough, so that the smooth side only can be used, thereby eliminating any 

 error that might arise from using two sides, if the slots should not be 

 accurately centered. 



rh 



Figure 2. — Steel Alidade with fixed Arms and saw-cut Slots 

 C03I.PA8S 



'No trough compass is inset into the board. An ordinary pocket com- 

 pass laid on a north line on the paper proved entirely satisfactory. 



SLOPS CARD 



The usual type of slope board advocated in the text-books on military 

 mapping, consisting of a long string with a weight on the end of it, at- 

 tached to the back of the board, was found in practice to be entirely un- 



