480 Irrigation and Drainage 



ing from this elevation that of the ^bottom of the 

 proposed ditch at this place, there is obtained 



10.13 7.12 = 3.01 feet, 



or the depth which the ditch must be dug at this 

 station, and it is the custom to write these depths on 

 the finder stakes, to serve as the guide to the ditchers 

 in digging, as represented in Fig. 157. 



These values are given in feet and hundredths 

 rather than in feet and inches, because it is much 

 simpler to make the calculations in this way. The 

 target -rod should be made to read in this way rather 

 than in feet and inches, and if the farmer makes his 

 own this may readily be done by first dividing the rod 

 into feet and then, taking a pair of dividers, set them 

 so as to space off ten equal divisions within each foot. 

 The tenths of a foot may then be subdivided in the 

 same manner into ten equal divisions, or hundredths 

 of a foot. 



Where a level without a telescope is used, the 

 measuring rod should be provided with a sliding 

 target, as shown in Figs. 153 and 158, which may be 

 moved up and down by the target man, as directed, to 

 mark the elevation indicated by the instrument. The 

 best target is provided with an opening in front of the 

 rod, which permits the figures to be seen at the junc- 

 tion of the cross lines of the target. 



In taking the elevations, the tar get -rod should 

 always be set upon the grade peg, and all subsequent 

 measurements in digging should also be made from 

 these pegs, which are driven in flush with the surface, 



