60 VOLUME OF WHOLE WOODS. 



the mean sample tree for each group, and selects an equal 

 number of these for each. 



The formula for K. Hartig's method is as follows : 



Sf Sf S' 

 As , -?, ?, . . . are not equal the one to the other, 



Oi Ss> So 



it follows that the sample trees must be measured and the 

 volume of each group calculated separately. By adding 

 together the volumes of the groups the volume of the whole 

 wood is obtained. This makes the method more laborious 

 than those of Draudt and Urich. 

 For example, see pp. 58 and 59. 



3. Comparative Accuracy of the several Methods. 



Guided by investigations made by various authors, it may be 

 said that in the majority of cases the difference between the 

 calculation made according to any one of the above-mentioned 

 methods and the results of actual fellings keeps within 2 per 

 cent., that the maximum error in the case of the method of the 

 arithmetical mean sample tree may be placed at 10 per cent., 

 and in the case of all the other methods at 5 per cent. 



If the results obtained in the examples used above are put 

 together, the following data are obtained : 



\r 4.1. i r i. T Volume Difference 



Method of inch classes : in c \ in %. 



Each inch class being calculated separately . = 3460 ... 



All sample trees being thrown together . . = 3554 ... +27 

 Method of four groups : 



Each group being calculated separately . . = 3471 . . . + '3 



All sample trees being thrown together . . = 3433 ... - -8 



Method of arithmetical mean sample tree . . . = 3482 . . . + '6 



Draudt's method = 3436 ... - 7 



Urich's method = 3458 ... - -06 



Hartig's method : 



Each group being calculated separately . . = 3402 ... - 17 



All sample trees being thrown together . . = 3457 ... - -09 



