PRESSLER S METHOD. 



41 



5. Pressler' s Method of ascertaining the Volume of Standing 



Trees. 



In order to avoid the determination and application of 

 average figures, Pressler devised the following method of 

 determining the volume by direct measurement on the tree : 

 He determines on the stem of the tree the point where the 

 diameter is one-half of that at chest-height ; let the distance 

 between the two points be h (Fig. 26). He 

 found that the volume of the stem above 

 height of chest is equal to f of the basal 

 area multiplied by h. 



If s = basal area at height of chest and 

 v. = volume, then 



v = _ x s x h. 

 o 



The above formula agrees very well with 

 the results of actual measurements. To 

 the volume thus ascertained has to be added 

 that of the piece below height of chest, 

 which Pressler assumes to have also a 

 cross section = s. If its length is equal 



to I, the volume of the whole stem conies 



_ -} 



to: 



O O / Q \ 



v = -xsxh + sxl= ~s[h + -l] 

 3 3 \ 2 / 



If now h + Z is put = H, the formula becomes 



...I.. 



Fig. 26. 



This formula gives the volume near enough for all practical 

 purposes ; to its amount has to be added the volume of 

 branches, whenever required. The drawback of the method 

 lies in the difficulty of ascertaining the point of the stem where 

 the diameter is equal to J of the diameter at chest-height. 

 Pressler ascertains it with an instrument specially constructed 



