COMPARATIVE ACCUEACY OF THE SEVERAL METHODS. 63 



If volume tables are used, the calculation is made according 



to the formula — 



V = n X s X h X f. 



Here s x h x f, equal to the volume of the mean tree, is 

 taken direct from the tables. 



4. Comparative Accuracy of tlie 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 : — 



These data show, that form factors for Scotch pine, obtained 

 from measurements in North Germany, are quite applicable to 

 woods in the South of England. Experience has also proved, 



