214 FORM CLASSES AND FORM FACTORS 



5. From the table of absolute form factors interpolate for the form factor required 

 to coincide with this form quotient. 1 



6. The basal area corresponding to the normal diameter at the stump is found 

 as follows: 



Do = normal stump diameter; 



D = D.B.H.; 



Bo = normal basal area at stump ; 

 £=basal area at D.B.H. 



If- D„ = 1.0pD, 



D 2 = 1.0p 2 D 2 , 



, .Bo-— 



ttZ) 2 



= 1.0p 2 



4 



= 1.0p 2 £. 



7. Total volume of the stem is then 



F=B„A/„ 

 =B1.0p%/ . 



8. Breast-high form factor is 



* = B~h 

 = 1.0p 2 /„. 



This series of breast-high form factors shows the diminution with increased 

 height, the cause of which is set forth in § 175. These form factors are given in 

 Table LXXXII, Appendix C, p. 497. 



Since form is best shown by taper tables, and volume is best obtained 

 directly from volume tables, the use of form factors in America has 

 but little practical application and has been adopted to a very limited 

 extent. Were the breast-high form factors more regular they would 

 serve as a means of constructing volume tables by graphic methods 

 (§ 138) in which the curves being comparatively straight could be 

 extended and interpolated with less chance for error than by the ordi- 

 nary methods. 



177. Merchantable Form Factors. Form factors based on the 

 merchantable contents of the tree in cubic feet, or upon the net cubic 



1 These absolute form factors are for the entire tree, but are based on the 

 theoretical stump diameter, hence are inapplicable for practical use. 



