When it seems likely that the upper-log average tapers assumed in these tables would result in excessive error, the volume in felled trees should be measured for comparison with the corresponding volumes in the tables. Log rules curved especially for use in volume-table construction are presented as tables 5, 6, and 7.
Measurement of about 50 trees of assorted diameters in each usable length class should be sufficient. Volume in one log trees will obviously remain unchanged. If a check shows the tables to be 3 percent high in each height class, they can be easily adjusted. Since the average increase or decrease in volume for a change of 1 percent in form class approximates 3 percent in tree volume, the simplest procedure is to adjust the form class. 1n this case the volume of a form class 78 tree would be obtained from the form class 77 table. Similarly, if a check revealed the tables 3 percent low, the volume of a form class 78 tree would be obtained from the form class 79 table. The refinement obtained by such a check will seldom be warranted. However, if the check is made the trees measured should be well distributed over the area to which the adjusted tables are to be applied.