146 A MANUAL FOR NORTHERN WOODSMEN 
Saw Kerf. This loss in logs of different sizes is pro¬ 
portional to the area of their cross-section, or to the square 
of the diameter. It varies in proportion to the thickness 
of saw kerf as well. As embodying an average of good 
present practice, ^ inch was allowed. 
Loss in Edging Lumber. This includes not only that 
portion of a log which is thrown away in the form of edg¬ 
ings, but also the fractions of inches in the width of boards, 
which in Dr. Clark’s studies were uniformly thrown off. 
It is counted to be in all logs proportional to the surface, 
or, what amounts to the same thing, to the diameter. 
Counting boards to be merchantable down to the size of 
2 ft. B. M., Dr. Clark found that an allowance of .8 foot 
board measure for each square foot of surface under the 
bark, or, what amounts to much the same, a layer .8 inch 
in thickness around the surface, would justly allow for 
this waste. 
Formula for the Rule. The above elements being put 
into mathemetical form with D representing top diameter 
inside bark, there is obtained for 4-foot sections the formula 
(D 2 X .22) — .71 D = contents B. M. 
Adaptation to Other Conditions. The product for other 
widths of saw kerf than J inch may be obtained by apply¬ 
ing the following per cents: 
For -gj inch kerf add 1.3 per cent. 
For ^ inch kerf subtract .5 per cent. 
For I inch kerf subtract 9.5 per cent. 
For T \ inch kerf subtract 13.6 per cent. 
For | inch kerf subtract 17.4 per cent. 
For ^ inch kerf subtract 20.8 per cent. 
Should the T Vinch allowance for shrinkage not be made 
in the mill practice in question, this may be allowed for 
in a similar way. According to Dr. Clark’s assumptions, 
each board with its saw kerf means lf\ inch in thickness 
taken out of the log. 
If mill practice in other ways is not so economical as 
the rule presupposes, that is to say, if logs are sawed 
with more waste in slab and edging than has been assumed, 
or if logs vary in taper and straightness from the standard, 
that is considered by Dr. Clark to be proportional to the 
