GENERAL FORMULAE FOR ALL LOG RULES 77 



the Doyle rule up to 28 inches, and substitutes the low values of the 

 Scribner rule above that point. 



The reverse of this process was adopted by the State of Louisiana 

 in 1914. The values of the Scribner rule below 28 inches were combined 

 with those of the Doyle rule for 29 inches and over, and the resultant 

 hybrid rule, known as the Scribner-Doyle rule is the official rule of the 

 state. 



The Doyle and Baxter rules were also combined, using the Doyle 

 values up to 19 inches, with those of the Baxter rule for the remaining 

 diameters. Both the Doyle-Scribner and the Doyle-Baxter are cut- 

 throat rules calculated to give the buyer the maximum advantage of 

 the defects of both rules. The Scribner-Doyle rule has no advantage 

 over the straight Scribner rule since most logs are below 28 inches in 

 diameter. 



73. General Formulae for All Log Rules. When log rules have not 

 been constructed by a formula, but from diagrams or mill tallies, no 

 formula can be found which will give the exact values of the rule. But, 

 consciously or not, the authors of log rules have attempted to deduct 

 the waste from saw kerf and from slabbing and edging and the average 

 results which they obtained, or the actual treatment of these two fac- 

 tors is revealed by reducing these rules to the nearest approximate 

 formula. 



The general form of such a formula is: 



B.M. = (aD 2 +&Z>+C)— 

 Y& 



in which aD* covers the per cent reduction of volume for sawdust after reducing the 

 square to a circle, bD gives the reduction of diameter or surface for slabbing and edg- 

 ing, while C is a constant added in an effort to correct irregularities in the rule itself. 



The factor — reduces square inches to board feet. 

 12 



Cubic rules converted to board feet correspond exactly to the formula, 



B.M. = (aZ> 2 )— 

 12 



or to 



irD 2 

 B.M. = (l-&)— — L. 

 4X12 



Perfect formula rules correspond to the formula, 



L 



or to 



B.M. = (oD 2 +&!>)- 

 \2i 



B.M. = (l-6) \ ' L. 

 ■ 4X12 



