98 



LAND DRAINAGE 



gineer's leveling rod. 



in grooves on the rod, or upon 

 guides, and is fitted with a clamp- 

 ing screw. The target is open in 

 the center to expose a portion of 

 the face of the rod. (See Fig. 40.) 



128. Using the level. 

 In using the level 



observe that: 



1. There is always a 

 starting point whose 

 elevation above datum 

 is known, or arbitrarily 

 established or, to put 

 it more correctly, be- 

 low which a datum 

 plane is arbitrarily es- 

 tablished. Ordinarily 

 in simple drainage 

 work, this arbitrary 

 height or elevation is 

 10 feet. 



2. There are one or 

 more other points 

 whose elevations are 

 not known, but which 

 it is desired to deter- 

 mine. The procedure 

 is about as follows : 



129. Setting up the 

 level. - - The level is 

 set up : 



1. At a convenient 

 within range of a 



