GENERAL METHOD OF SAMPLE TREES. 45 



/. — The Height is a Function of the Diameter. 



1. Descriptum of the General Method. 



a. Fonnafion of Diameter Glasses. 



The number of classes depends on the difference between 

 the largest and smallest trees of a wood and the desired degree 

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

 that is to say, either 1 inch, 2 inches, 3 inches, etc., or part of 

 an inch. For the purpose of forest working plans in Europe, 

 each class comprises 1 or 2 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 li inch; the second that from Ih to 2^ inches, etc. 

 For scientific investigations the classes may be further reduced 

 to a part of an inch. 



h. 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 



