54 VOLUME OF WHOLE WOODS. 



volume of all the sample trees, v x X n l x 'op + r 2 x n ., x 'op + 

 . = v t then 



V X *op = v 

 and 



x 



It happens generally that the number of sample trees in each 

 class contains a fraction of one. Such fractions are eliminated 

 by considering *51 as a full sample tree, and by neglecting '50 

 and under, taking care that the total number of sample trees is 

 as nearly as possible correct. The result of this operation is, 

 that the original proposition is no longer absolutely main- 

 tained ; in other words, the volume of the actual sample trees 



does no longer represent the true value -=75^* To avoid this 



1U(J 



inaccuracy, Draudt introduces the basal area of the whole 

 wood =$, and of the sample trees =s, by saying: 



s : S = v : V, 

 and 



V=vx S . 

 s 



This formula is used to calculate not only the whole volume, 

 but also that of timber and firewood separately. 

 The advantages of Draudt's method are : 



(1) That the sample trees can all be worked up together; 



and 



(2) That it yields a high degree of accuracy. 



Its drawbacks are : 



(1) That in rounding off the number of sample trees in each 



class, inaccuracies are likely to be introduced ; and 



(2) That frequently no sample trees at all are taken from 



classes which contain only a small number of trees. 



The larger the wood, that is to say, the greater the number 

 of trees in the several classes, the more accurately the method 

 works. 



Example. The following example will further explain the 



