LEVELING 101 



4.95 feet above the point at which the rod was held. Let 

 us suppose also the height of the point at which the 

 rod is held to be 11.35 feet above datum. If, now, we 

 add 4.95 feet to 11.35 feet, we have 16.30 feet as the 

 height of the instrument above datum. 



135. Elevation of other points. The height or ele- 

 vation of other points within range of the level are de- 

 termined in the following way : 



1. The rodman carries the rod and holds it, face to- 

 ward the level, upon one of the points whose height is 

 sought. 



2. The telescope is turned toward the rod in its new 

 position and focused to bring out, most clearly, the figures 

 on the face of the rod. The reading is taken as in (133) 

 above and recorded. 



136. Fore-sight reading and its use. This reading is 

 called a fore-sight, which is the name given to any reading 

 taken at the point whose elevation is to be determined. 

 Let us suppose that this fore-sight reading is 4.22 feet. 

 It means that the point at which the rod is held, and whose 

 elevation is sought, is 4.22 feet lower than the instrument, 



4.22 feet nearer the datum plane than is the instrument. 

 If, then, we subtract 4.22 feet (the fore-sight reading) 

 from 16.30 feet (the height of the instrument), we obtain 

 12.08 feet as the elevation of the new point. 



In like manner the rod should be placed at other points 

 within the range of the instrument, and fore-sight readings 

 taken. In each case, subtracting its fore-sight reading 

 from the height of the instrument gives the elevation 

 of the point at which the fore-sight reading was taken. 

 Let us suppose three other fore-sight readings are taken 

 at three other points, respectively, and that these three 

 readings are 3.75 feet, 3.06 feet and 3.11 feet. 



