62 THE WOODSMAN’S HANDBOOK. 
timber to be estimated is the same as that of the trees from which 
the table was constructed. Frequently the average heights of the 
trees used in constructing the table are not given, and in this case 
the table is comparatively worthless. If, for example, the tables 
were based largely on tall trees, they would not be used where the 
trees are short. This objection is largely obviated by making 
local tables for restricted areas on which the general conditions 
for growth are fairly uniform. | 
Volume tables for trees grouped by diameters alone are designed 
primarily for commercial estimating in board measure. 
VOLUME TABLES BY DIAMETER AND STANDARD LOG LENGTH. 
A further grouping of the trees is necessary for very close deter- 
mination of volume, because in tables grouped by diameter alone 
all trees are averaged by diameters regardless of height or length 
of merchantable timber. Thus one-log trees are averaged with 
three-log trees, or even five-log trees, of the same diameter. In 
order to secure greater accuracy, volume tables based on trees 
grouped by diameters and number of logs were devised. Such 
tables are in actual use by cruisers in tall timber where a standard 
log length—for example, 16 feet—may be used in the estimate of 
the number of logs. 
To construct a volume table for trees grouped by diameters and 
number of logs, a large number of felled trees are measured and 
their volumes computed. The trees having the same number of 
logs are then grouped together, and the average volumes of trees of 
different diameters are determined for one-log, two-log, and three 
or four log trees. If the volumes do not increase regularly with 
increase of diameters, the irregularities are evened off by graphic 
interpolation, in which the actual values are set down on cross- 
section paper and a curve is plotted to give the average value at 
each diameter. 
