FORM FACTORS FOR BOARD FEET 225 



Frustum form factors can be computed if desired, in cubic feet. 

 For board feet, any log rule may be used as desii-ed. 



A shorter but less satisfactory method is to first determine the top 

 diameters of the frustums to be used in the base table and prepare the 

 table of frustum volumes; second, to compute the arbitrary form 

 factors which are obtained by dividing the average volumes of the trees 

 in each class by the volume of the proper frustum, disregarding the 

 possible difference in top diameter and average height for the class; 

 and from these factors, to construct the volume table. This method 

 works best when fixed top diameters are used in logging and the dif- 

 ferences in top diameters between frustums and trees is small. 



The method of frustum form factors has resulted in such a marked 

 increase in accuracy and economy in preparation of standard volume 

 tables based on merchantable board-foot contents that it has practically 

 superseded the standard methods of preparing these volume tables, 

 and until total height and tables based on form classes supersede the 

 use of merchantable heights in timber estimating, this method will 

 continue to be used extensively. 



186. Other Merchantable Form Factors for Board Feet. Merchant- 

 able form factors based on the volume of a cylinder whose height equals 

 the merchantable length in the tree have been proposed by E. I. Terry. 



Merchantable volume tables based on the contents of frustums of 

 paraboloids whose top diameters equal one-half D.B.H., scaled in 16- 

 foot logs, have been computed by the Forest Service. These correspond 

 in principle to the basic volumes of frustums of cones, and can be used 

 for calculating form factors in the same manner, but offer no special 

 advantage over the frustums of cones for the purpose required. 



References 



A New Method of Constructing Volume Tables, Donald Bruce, Forestry Quarterly, 



Vol. X, 1912, p. 215. 

 The Use of Frustum Form Factors in Constructing Volume Tables, Donald Bruce, 



Proc. Soc. Am. Foresters, Vol. VIII, 1913, p. 278. 

 Further Notes on Frustum Form Factor Volume Tables, Donald Bruce, Proc. Soc. 



Am. Foresters, Vol. X, 1915, p. 3l5. 

 The Use of Frustum Form Factors in Constructing Volume Tables for Western 



Yellow Pine in the Southwest, Clarence F. Korstian, Proc. Soc. Am. Foresters, 



Vol. X, 1915, p. 301. 

 Top Diameters as Affecting the Frustum Form Factor for Longleaf Pine, H. H. 



Chapman, Proc. Soc. Am. Foresters, Vol. XI, 1916, p. 185. 

 Frustum Form Factors of Hard Maple and Yellow Birch, B. A. Chandler, Bui. 210, 



Vermont Agr. Exp. Sta., May, 1918. 

 A Formula Method for Estimating Timber, E. I. Terry, Journal of Forestry, 



Vol. XVII, 1919, p. 413. 

 Comment on Above, Donald Bruce, Journal, Vol. XVII, 1919, p. 691. 

 Further Comment, E. I. Terry, Journal, Vol. XVIII, 1920, p. 160. 



