90 



DETERMINATION OF THE INCREMENT 



Then the hasal area .s, at -^ , is ascertained, either In' makino; a 



cross section at the sjDot, or hj ascertaining the breadth of the 

 last n rings with the increment borer, thus ascertaining the 

 diameter, which the tree had n years ago. In either case, 



Fij?. 32. 



the diameter increment must be measured in several places of 

 the circumference, so as to obtain the mean. 



In order to simplify the operation, Pressler proposed to cut 

 off a length corresponding to n years' height growth in the 

 first place, and then to measure the basal area in both cases at 



-. (See Fig. 33.) He ol)tains the increment according to the 



A 



formula : 



7 = ,S X /( - .5 X // = (S - s) h. 



The error due to omitting the top is said to be compensated 



for l)y ,S' being taken somewhat below -. 



