186 



VOLUME TABLES FOR BOARD FEET 



such tables, needs special emphasis. If a large top diameter is adopted, 

 the merchantable height is correspondingly less for trees of the same 

 total height and form. A tree 100 feet high may have five logs, 16 

 feet long, if cut to 10 inches, but if cut to 16 inches instead, it may be 

 only a four-log tree. A 6-inch top may in turn 

 give 88 feet or 5| logs from the same tree. Thus 

 top diameter increases as merchantable length 

 diminishes. Whatever coordination between 

 these two variables is adopted in constructing 

 the volume table will have to be used in applying 

 it; i.e., the same top diameters used for the 

 table must be used as the basis of merchant- 

 able heights in timber estimating. Failure to 

 observe this rule may result in serious errors 

 and has sometimes brought the use of such 

 volume tables into disfavor among practical 

 cruisers. 



The results of such lack of coordination are easily- 

 illustrated, by comparing the volumes of trees, when 

 divided into 16-foot cylinders and scaled as logs. 

 Since the frustum of a cone is a regular solid resembling 

 the merchantable portion of the bole, it serves to illus- 

 trate the principle in question. Assume that a 6-inch 

 top has been adopted as a standard, and all trees meas- 

 ured to that point. 



A four-log tree, 15 inches at the top of the first log, 

 inside bark, is assumed to have 3 inches taper per log. 

 The volume of this tree, by the International log rule, 

 will then be 



Fig. 31.— Cause of 

 errors in use of vol- 

 ume tables, when 

 based on merchant- 

 able heights and 

 fixed top diameters. 



In estimating, if this table is to be used, the only 15-inch four-log tree whose 

 volume can be correctly measured is one which tapers 3 inches per log, and hence 

 has a 6- inch top diameter. But the cruiser may fail to observe the same coordi- 

 nation between merchantable length and top diameter, and may tally a 15-inch tree 

 which tapers 2 inches per log, as a four-log tree. The dimensions of this tree up to 

 the top of the fourth log are 



