LEVELING 



103 



2. The back-sight was taken at point 1. It is always 

 taken at a point whose elevation has been established. 



3. Each fore-sight reading is recorded after the point 

 at which it was taken. 



4. In making computations for determining the elevation 

 of the other four points, the back-sight reading 4.95 feet 

 is added to the elevation of point 1, which in this case is 

 11.35 feet. This gives 16.3 feet as the height of the in- 

 strument above datum and this is introduced after the 

 back-sight reading under height of instrument, as appears 

 in Table IX. 



5. The elevation of each point is found by subtracting 

 its fore-sight reading from the height of the instrument, 

 and when all the elevations are thus found and introduced 

 the completed table appears as is shown in Table IX. 



TABLE IX 

 TABLE VIII COMPLETED 



140. Moving and resetting the instrument. If there 

 are other points too high, or too low, or too far away to 

 fall within the range of the level, it must be moved and 

 set at a new place, so that one or more of the other points 

 shall fall within its range, and such that one of the points 

 whose elevations have already been found shall also lie 



