GENERAL METHOD OF SAMPLE TREES, 45 



of accuracy. As a rule all classes are given the same extent, 

 that is to say, either one inch, two inches, three inches, etc., 

 or part of an inch. For the purpose of forest working plans 

 in Europe each class comprises one or two inches ; in India 

 frequently as yet 6 inches. 



The calliper used in measuring the diameters should have a 

 rounded-off scale, as described in Chapter I., that is to say, in 

 the case of inch classes, the first should comprise the space 

 from J" to If inch ; the second that from 1 J to 2J 

 inches, etc. 



For scientific investigations the classes may be further 

 reduced to a part of an inch. 



b. Height and Manner of Measurement. 



All trees must be measured at the same height, the latter 

 being so chosen, that the place of measurement falls above the 

 irregular swelling frequently observed near the foot of the tree ; 

 at the same time the height should not be so great that it 

 becomes difficult for an ordinary-sized man to measure accu- 

 rately. Whenever practicable, the height should be the height 

 of chest of an average man. 



In executing the measurement all the precautions indicated 

 in Chapter I. must be duly taken, so as to obtain as accurate 

 results as possible. More especially any irregularity in the 

 shape of the sections must be duly considered. Where the 

 section differs systematically from that of a circle, either two 

 diameters at right angles must be measured, or the direction of 

 measurement changed from time to time. For instance, after 

 a certain number of stems have been measured with the face of 

 the measurer to the east, an equal number must then be 

 measured at right angles, that is to say, with the face of the 

 measurer towards the north or south. Or the change can be 

 made at alternate trees. In this manner average diameters are 

 obtained. 



