WEISE'S METHOD 



431 



Hence by this rule the average tree is one of [ 2 inches 

 diameter. 



Having ascertained this, the height of several trees having 

 this diameter is accurately measured, and the average height 

 arrived at ; then the average form factor, for the species of 

 tree having this height, is ascertained from tables ; and then 

 the contents of this average stem are found, e.g., basal area x 

 height x form factor ; and the contents of the whole area are 

 equal to the contents of the average stem x number of stems 

 on the area. 



If the crop be mixed, the species of trees must be kept 

 separate ; and their contents separately computed. 



Whenever there is no objection to the contrary, a few of 

 the average stems should be felled, and their contents accu- 

 rately measured ; for by this means, still greater accuracy 

 will be obtained, and the use of an average form factor 

 dispensed with. 



A method giving still greater accuracy is to find the basal 

 area and height for each class ; and then the contents of all 

 the trees in each diameter class ; and finally the contents, on the 

 whole area, by adding the contents of each class together thus : 



