280 A MANUAL FOR NORTHERN WOODSMEN 
The remaining figures illustrate variation of form ant 
irregularity. Nos. 11 and 12, having the same diametei 
breast high and also at the top of the logs used, are yei 
13 per cent apart in contents, while the second pair o; 
matched trees differ by .19 per cent, of the average valut 
in each case. The taper of the body of these trees it 
regular, however; the variation is in the butt and top 
log sections, the former being far more significant. Tree* 
Nos. 15 and 16 show some real irregularity, though noth 
ing extreme. Much wider departures from type thai; 
any of these could in fact be chosen. 
In conclusion, a contrast will be drawn between present 
commercial methods and the use of volume tables. In 
the construction of these it is customary to throw out 
swell butt and other abnormality of form, and, that 
done, the tables derive strength from the law of averages, 
Single trees may depart from the type and a certain 
amount of variation goes with age, but the table, based 
on a large number of trees and applied to large numbers, 
if that is done in the same way the measures behind the table 
were taken, gives results that are trustworthy within 
reasonable limits. Present-day commercial estimates may 
be equally correct, but that depends on a different thing 
— on the ability of the cruiser to size up each tree as 
seen, on the basis of his training of every description. 
