STATE BOARD OF FORESTRY. 



CONSTRUCTION AND UNDERLYING PRINCIPLES OF 

 LOG RULES. 



LOG RULES IN GENERAL. 



About forty-five log rules have been devised within the last seventy- 

 five years for the measurement of sawed lumber from logs of different 

 sizes, and the values shown by these different rules cover an enormous 

 range. It is safe to say that 90 per cent of them are so constructed that 

 at best they are of value only under the conditions of the locality where 

 they were first employed, and there is no means whereby they can be 

 intelligently corrected for other conditions. Such is the case with all 

 log rules based upon diagrams showing the amount of lumber in logs 

 after allowances have been made for slabs, saw-kerf, etc. Such is the 

 case with all log rules obtained by correcting these rules or combining 

 them for others. Also rules resulting from actual experience at saw- 

 mills have the same objections. They bear the prints of local conditions 

 and, due to the method whereby they came into existence, they can 

 never be anything more than local, and can only be applied to milling- 

 conditions similar to those existing at the mills where they were first 

 constructed. 



The only logical way of constructing a log rule which will be flexible 

 and which will adjust itself to universal conditions, is to so construct it 

 that the underlying, fundamental principles are so segregated as to 

 make them independent of one another, and to have them so worked 

 together as to give the aggregate result of all factors, which will be in 

 all cases proportional and equal to the volume of the manufactured 

 product. There are several distinct principles underlying the measure- 

 ment of lumber which logs of different sizes will produce, Avhich cannot 

 be overlooked in any rule that is destined to become a correct universal 

 measure. Such a rule must embody the principle that the slabs which 

 cover the material, or part of the log which is to become the finished 

 product, should be allowed for by making the allowance proportional to 

 the barked area of the log. The slabs are the covering, as it were, which 

 necessarily has to be removed in order to get to the part of the log 

 that produces lumber, and they should not be. and are not, cut any 

 thicker from large logs than from small ones. The best material con- 

 tained in the log usually lies nearest to the bark, and it is greatly to the 

 ;idvantage of the millman not to waste any of his best grades. 



Several log rules in most common use today do not embody the above 

 principle. The Spaulding Log Rule, which is the statute rule of Cali- 

 fornia, does not adhere to it. The Scribner Rule, which is the official 

 rule of the Forest Service, U. S. Department of Agriculture, and of 

 several states, does not take it into consideration, and instead of having 

 the volume of slabs proportional to the barked area of the logs, they 

 have them proportional to the total volume, as will be shown further on. 



It would not be any more absurd if one tried to figure the number of 

 board feet necessary to side up a house by figuring the volume of the 

 house instead of its lateral surface. A definite per cent cannot be 

 riven as indicating the relation of slabs to trees of different volume, 

 any more than a definite per cent can be given as indicating the rela- 

 tion of all lateral surface to the volume of houses of different dimen- 



