TEXTBOOK OF LANDSCAPE GARDENING 
and hundredths. It is usually desirable further to have a meas- 
uring tape or chain. 
ve 
Fig. 18, Usinc THe Farm Leven 
Operation 
The operation of leveling consists primarily in determining 
the difference in elevation between two given points. The instru- 
ment is set up at some third point from which the two points A and 
X to be compared are visible. When the level tube has been brought 
to a horizontal position, the leveling-rod is placed with its zero mark 
upon the first point, A, the elevation of which is known, and a read- 
ing is made. This is called a back sight, and the resulting figures 
tell the height of the telescope tube (line of collimation) above the 
point A. If this point A is one whose elevation has been deter- 
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