The Abney Hand Level. 



365 



or rise per chain or unit of 

 horizontal distance along 

 the slope of the given de- 

 gree or per cent, on the 

 map sheet. 



Thus the draftsman does 

 not have to calculate the 

 distance to the position of 

 the contours. He scales the 

 distance directly with this 

 rule and the whole opera- 

 tion is performed with 

 speed and precision. The 

 camp draughtsman is not 

 called upon to do much 

 arithmetical work. The 

 office work is done by 

 graphic methods and speed 

 will become a matter of 

 practice. Arithmetical cal- 

 culations are tedious and 

 speed is very much influ- 

 enced by mental fatigue. 

 Using this rule the eleva- 

 tions of the slope stations 

 can be obtained by reading 

 the drop in feet from the 

 rule and adding or subtract- 

 ing the difference in eleva- 

 tion to the elevation of the 

 preceding slope station. 

 The position of the contour 

 can be read directly from 

 the rule. 



In order to explain the 

 character of this rule and 

 its application the whole 

 operation is here explained 

 in full; applying to the 

 strips shown in Figure 4. 



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