42 BULLETIN 139, U. S. DEPARTMENT OF AGRICULTURE, 
To construct a volume table froni the upper diameters or tapers given 
in Table 25, the average top diameter to which trees are utilized must 
be known. In species possessing a regular form this may be a fixed 
limit, as 6 inches, regardless of the size of the tree. But where 
utilization is not close, and tops are hea^y, with large limbs, the di- 
ameter limit in the top will increase with the diameter of the tree. 
With this top diameter determined, the taper table will indicate the 
merchantable length for each diameter and height class to the near- 
est 8-foot length. For board feet, adapting a 16-foot log, the up- 
per diameters of each log in the tree enable one to secure the scaled 
contents by the desired log rule. 
The number of standard railroad ties or products of other known 
dimensions may also be found for trees of any size from this table. 
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