124 



LAND DRAINAGE 



height of instrument and elevation of stake in the proper 

 places. 



At this point compare the results with those recorded 

 in Table XV below. If they do not agree in all cases 

 go over the work to discover and correct the difficulty. 



TABLE XV 



SAME AS TABLE XIII ELEVATIONS INTRODUCED 



167. A comparison of tables. The data shown in 

 Table XIV are those obtained for the same drain with a 

 high-grade instrument. Observe that the single back- 

 sight reading is introduced on the line of stake 1. The 

 elevation of stake 1 is 10 feet, as in the other case. The 

 back-sight reading is 6.23, which, added to the elevation 

 of stake 1, gives the height of the instrument as 16.23. 

 Subtracting any fore-sight reading from the height of 

 the instrument gives the elevation of the stake at which 



