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. 



