228 



THE MEASUREMENT OF STANDING TREES 



for measuring the diameter of standing trees and their use is necessary 

 in taking taper measurements on down timber which cannot be meas- 

 ured with diameter tape. The standard type of calipers for eastern 



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Fig. 39. — Calipers used in measuring the diameters of standing trees. 



hardwoods has a beam 36 inches long with arms one-half that length. 

 A smaller type may be used for trees whose diameter does not exceed 

 2 feet as in spruce or second-growth timber. The standard calipers 

 have a beam graduated on both sides to inches and tenths, and two 

 arms, one of which is bolted to the end of the beam, the other a sliding 

 ^^ arm, the beam 



passing through a 

 slot. 



Fig. 40 indicates 



the construction 



of this arm. The 



essential feature 



is that when not 



pressed against 



the tree, the arm 



is easily moved 



along the beam — 



but when in use 



it takes a position at right angles with the beam and parallel to the 



other arm. The position of this arm is adjustable by the movement of 



the screw (o) which sets a movable plate. 



In use the arms must be at right angles to the beam. If warped or 

 out of adjustment, corresponding errors in measuring diameters will 

 occur. The correct diameter can be obtained only by holding the cali- 



Fig. 40.- 



-Construction of calipers, to secure adjustment of 

 movable arm at right angles to bar. 



