A Comparative Study of Log Rules. 793 



Table 3, showing the mean over-run in board feet for logs of 

 the several groups, discloses the fact that the Scribner rule is 

 less reliable than the "Universal." The mean over-run for the 

 Scribner is about double that of the ''Universal" in all groups 

 excepting Groups V and VII. This confirms the figures shown 

 in Table i, where the percentage of over-run on all logs is nearly 

 in the same proportion for the two rules. 



It is acknowledged that in a study of this kind there is some 

 opportunity for the lack of skill on the part of the scaler in dis- 

 counting for defects to affect the figures to such an extent that 

 no definite conclusions could be reached. If the full scale were 

 allowed on defective logs, then the mill-cut would be quite likely 

 to fall short of the scale, and conversely, if too liberal a discount 

 were made the mill-cut would greatly exceed the scale. In the 

 present instance the conditions were favorable to a high degree 

 of accuracy, because the logs were most of them sound, and the 

 task of scaling called for the exercise of judgment chiefly in 

 the matter of determining the average diameter, and proper al- 

 lowances for slight crooks in the logs. 



The general conclusions reached in this comparative study 

 of the two log rules may be stated as follows : 



(i) Both the Scribner and the "Universal" Rules give a sound 

 log less than can be produced from it under favorable con- 

 ditions. 



(2) Both rules fall short by larger percentages in the small 

 logs than in the large logs. The scales apply with the greatest 

 accuracy in logs of medium size, that is, from 16 to 26 inches in 

 diameter. 



(3) With sound logs, the mill-cut may be expected to over- 

 run the Scribner scale by about 10% and to over-run the "Uni- 

 versal" scale by about 5%. 



(4) All things considered, the "Universal" Rule will give bet- 

 ter results than the Scribner Rule, but both run low for the logs 

 of small diameters. 



Note. — The "International" Rule, as printed by Dr. J. F. Clark in 

 "Forestry Quarterly," Vol. IV, page 79, may be adapted to allow for a 

 saw kerf of % inch by applying a reducing factor of 9.5%. This was 

 done, and the logs by this scale would yield a total of 7,435 board feet, 

 or only 2^% less than the actual mill cut. It may be said, therefore, 

 that the "International" Rule, when adjusted to allow the proper amount 

 for saw-kerf, will undoubtedly give very good results. 



