44 THE MEASUREMENT OF LOGS— BOARD-FOOT CONTENTS 



cylinder, and measured at its upper or small diameter, and the sum of 

 volumes of these cylinders gives the scale of the long log. 



The shorter these scaling lengths are made, the larger the total scale 

 of the log, but the maximum scaling length must not be shorter than the 

 average length of the lumber sawed. In log rules, figures for lengths 

 up to 40 feet may be given, and scaling practice often corresponds, but 

 in selling logs the U. S. Forest Service limits the scaling length to 16 

 feet, which is a standard commonly accepted by timber owners. 



44. The Introduction of Taper into Log Rules. With the increase 

 in utilization, much of the lumber formerly Wasted in slabs is now secured 

 as short lengths. All log rules in commercial use ignore this product 

 and treat the logs as if cylindrical, up to the maximum scaling length. 

 To overcome this drawback and include the products from slabs or taper 

 without requiring the measurement of logs in separate very short sec- 

 tions, the International log rule was constructed, 1 based on the principle 



Taper, 2 inches in 16 feet. Vertical scale exaggerated. 



Fig. 5. — Short versus long sections in measuring log contents and in constructing 



a log rule. 



of building up the scaled volume of a log from shorter cylindrical sec- 

 tions. These short cylinders are 4 feet long and each successive cylinder 

 is increased by |-inch in diameter. The scaled contents of each short 

 section is determined, and the sum of these sections gives the scale of 

 the log as given in the log rule. The soundness of this method depends 

 upon demonstrating that the average taper of most logs is not less 

 than that used in the rule, namely, 2 inches in 16 feet. This holds good 

 for most Northern and Western species, but for Southern pines the taper 

 does not always equal this figure. To guard against excessive error 

 from tapers differing from the rate used in the rule, the maximum 

 scaling length is limited to 20 feet. 



If the log in Fig. 5 is regarded as a 64-foot log, scaled in four 16-foot lengths by 

 any commercial log rule, the scaling diameters are taken at A, B, C and D. The 

 gain in scale is caused by inclusion of the shaded portions. 



1 The Measurement of Saw Logs, Judson F. Clark, Forestry Quarterly, Vol. IV, 

 1906, p. 79. 



