LEVELING 



87 



all other elevations are deduced from them. The method 

 depends on the fact that all backsights are additive (+) 

 quantities, and all foresights are subtractive ( ) quantities. 

 The accompanying level notes are checked as follows: The 

 elevation of the bench mark at station is 100.00 ft., to which 

 all backsights, or + readings, are to be added and from this sum 

 all foresights, or readings, are to be subtracted. The sum 

 of the backsights, with elevation of bench mark at Sta. 0, is 

 122.59. Sum of foresights on turning points is 24.27, and dif- 

 ference is 98.32 ft., the elevation of the last turning point. 

 When a page of level notes is filled, the notes should be checked 

 and a check-mark placed at the last height of instrument or 

 elevation checked. When the work of staking out or cross- 

 sectioning is being done, the levels should be checked at each 

 bench mark on the line. After each day's work, the leveler 

 must check on the nearest benchmark. 



Profiles. A profile represents a longitudinal section of the 

 line of survey. In it all abrupt changes in elevation are 

 clearly outlined. Vertical and horizontal measurements are 

 usually represented to different scales, to render irregularities 

 of surface more distinct through exaggeration. For railroad 

 work, profiles are commonly made to the following scales: 

 horizontal, 400 ft. = 1 in.; vertical, 20 ft. = 1 in. 



10 



A section of profile paper is shown in the accompanying 

 diagram. Every fifth horizontal line and every tenth vertical 



