LAYING OUT A DRAIN OR SYSTEM 133 



top against the line, tell when he has brought the bottom 

 of the ditch to the proper depth. 



173. Determining height of bar above grade stake. 

 The height of the grade bar above any stake is found by 

 subtracting the depth of the ditch at that stake from the 

 height the line is to stand above the bottom of the ditch 

 (5.5 feet in common practice). These heights are shown 

 in column 10, Table XVI. Verify the figures in column 

 10 from those in columns 8 and 9. 



174. Using the data. When the work is to be super- 

 vised closely by the person developing the data, it is 

 sufficient to rely upon the tables as they are completed. 

 In some cases the depth of ditch, height of grade bar, 

 with the distance of the grade stake from the outlet, and 

 other data, are recorded upon its finder. Sometimes 

 this information is introduced upon the profile diagram 

 used in determining the grade, depth of ditch, and so on 

 or upon one drawn for the purpose. (See Fig. 49.) 



