20 



LOG RULES 



tables in which the values vary more or less regularly according to some 



definite law. 

 Illustration 1. — Extension by prolonging a curve. 

 Explanation. — The Drew Rule has been chosen for this illustration because 



it gives values only for logs above 20 feet in length. The object will be to 



extend the values for 16-inch logs so that they may be scaled down to 10-foot 



lengths. 



Directions : 



A. Method of Procedure. 



1. With lengths in feet as abscissae and volumes in board feet as ordinates, 

 plot the following values for 16-inch logs by the Drew Rule. 



2. Extend the curve backward to 10 feet. Be careful that the extended 



portion of the curve follows the spme general trend as the original 

 curve. 



3. Read values from the curve for lengths from 20 feet down to 10 feet 



in 2-foot classes and tabulate. 



4. The values for other inch classes may be extended backward in a sim- 



ilar manner, and the values thus secured tabulated. 

 Illustration 2. — Extension by interpolation. 



Explanation. — The Vermont Rule gives the following board foot contents 

 for 16-foot logs. 



The object will be to extend this rule so that volumes for logs "d to 36 

 inches in diameter can be obtained. 



