METHOD OF ESTIMATING TIMBER 161 



height is not exactly in that ratio, but here again the error is inappre- 

 iable except for timber having a wide height range within each diameter 

 class. 



I believe that both the objections raised by Bruce may be met by 

 employing several board-foot form factors for each diameter, say, for 

 every 30 feet of merchantable length or for each log-length. In my 

 article I made the following statement : "Whether this method will 

 give accurate results when applied to the large timber of the Pacific 

 Coast may depend chiefly on whether one merchantable form factor 

 will serve for each diameter class, irrespective of length. If the form 

 factor varies considerably with length, then several values of b for each 

 dimeter class would have to be computed." 



By using the "short-cut" method of computing the board-foot form 

 factor suggested by Sparhawk in his comment on my article, the time 

 and labor involved in computing such a table of factors will be com- 

 paratively slight. 



For small to medium-sized timber and for timber where the height 

 is, even roughly, a function of the diameter, I believe that one value 

 of b for each diameter class will give accurate results. My computa- 

 tion of the board-foot form factors for the western yellow pine was 

 based upon 815 trees, rather evenly distributed among the diameter 

 classes from 12 to 36 inches. The total actual scale of these 815 trees 

 is 530,880 board feet. After having computed the board-foot form 

 factors, I worked up the scale of these trees by using the factors and 

 the total length of each diameter class (V = &H). The result was 

 530,580 l)oard feet, or a difiference of about one-twentieth of one per 

 cent. That seemed to me to prove at least the theoretical accuracy of 

 the method. 



