MEASUREMENT OF THE DIAMETEK. 



(b.) Owing to the presence of a rough bark, the measured 



girth is too large, 

 (c.) Irregularities in the tree are difficult to avoid. 

 (d.) The tape is frequently not applied at right angles to the 



axis of the tree. 

 In order to avoid some of the disadvantages of tape measure- 

 ments, a thin string is sometimes used, which is then held 

 parallel to a graduated tape or rule. In this way more 

 accurate results may he obtained, but the procedure takes 



Vertical Section of ilovable 

 i Arm. 



Fig. 1. — Friedrich's Calliper. 



more time, and is therefore not employed, where large numbers 

 of trees have to be measured. 



2. Instruments for the JSIeasurcment of the Diameter. 

 The diameter of sections of trees is measured with an 

 ordinary rule or a tape ; in all other cases the calliper is used, 

 or sometimes the tree compass. 



a. Tlte Callqier, or Diameter Gauge. 

 It consists of a graduated rule and two arms. Of the latter, 

 one is fixed at one end at right angles to the rule, so that its 



