66 THE CONSTRUCTION OF LOG RULES 



This rule compares favorably with other theoretically accurate rules except that 

 it shaTes the common fault of neglecting taper. Mr. Daniels states (1917), that he 

 favors the use of the Champlain rule as the more accurate of the two. 

 Wilson Log Rule, 1825. 



7r(£>-l) 2 £ 



B.M. = .807- — . 



4 12 



By Clark Wilson, Swanzey, N. H. Originated in 1825, and computed for J-inch 



boards. Now obsolete. This was unquestionably the first formula rule. The author 



was a mathematician, and "estimated the difference in yield in gain of the large 



logs over the small ones, and then calculated the intermediate spaces by nearly 



regular integral differences as logs increase in size. The author intended it for 



f-inch boards. It is recorded that E. A. Parks later used it for 1-inch boards, which 



use resulted in a lawsuit." (John Humphrey, Keene, N. H.) 



Preston Log Rule, An Old Rule. 



t(D-1.75) 2 L 



Large logs, B.M. = .80- — . 



4 12 



Small logs: B.M.^SO ""^ -1 5 — . 

 4 12 



Still used in Florida. Known locally as a seller's rule. Sold in Jacksonville, Fla., 



by H. & W. B. Drew Co. 



Thomas' Accurate Log Rule. 



„„ „tt(D-1) 2 L 

 B.M.^.78- 5 — 



12 



For |-inch saw kerf. Also computed for 5-inch kerf. 

 Click's Log Rule, 1909. 



B.M.^,764^- 1 - 25 ^. 

 4 12 



By A. C. Click, Elkin, N. C, 1909. This rule was based on 1-inch boards averaging 

 6 inches in width and makes reduction for saw kerf of J-inch as per the formula 

 (§ 58), used by McKenzie. Other rules for different widths of saw kerf were worked 

 out by the author. (Forestry Quarterly, Vol. VII, 1909, p. 145.) 



Carey Rule, Date Unknown. This was a caliper rule to be applied to middle 

 diameter, and was used for round edge boards 1-inch thick. The values given are 

 almost identical with the Wilson rule. Formerly used in Massachusetts. 



Clement's Log Rule, 1904. 



B.M.= 



..■D*\ \L 



This log rule illustrates the use of a rule of thumb, based on correct mathematics. 

 The above formula is expressed thus: Multiply half the diameter by half the circum- 

 ference, then subtract half the circumference. The remainder will be the total 

 amount of feet board measure, in a 16-foot log. 

 This becomes: 



B.M. = (.7854D 2 -1.57D)— , 

 'l6' 

 from which the above formula is derived. 



With the exception of the Preston, none of these rules is in commercial use. 



