72 THE CONSTRUCTION OF LOG RULES 



altogether. No owner of small logs or of young standing timber can afford to sell 

 on the basis of a scale or estimate made by the Doyle rule. As it stands, this rule 

 is a serious obstacle to the profitable marketing of second-growth timber, hence to 

 the practice of forestry. 



67. The Construction of Log Rules Based on Diagrams. In con- 

 structing log rules based on diagrams (§ 55), the quantity of 1-inch 

 boards contained within a given diagram may vary, due to four different 

 factors. The first is whether a 1-inch board or a saw kerf is placed on 

 the center line. For some diameters the one method gives the most 

 lumber, for others the alternate plan, depending upon the relation of 

 the total diameter to the sum of the diameters of boards plus saw kerf. 

 The second factor is the minimum width of the boards to be sawed. The 

 narrower the board, the greater will be the product from circles of a 

 given diameter. The third source of variation lies in the choice of 

 plotting all boards as if slash sawed, or else arbitrarily choosing a given 

 method of sawing around or squaring the log on the diagram, with 

 boards taken from the slabs. The fourth factor is the acceptance or 

 rejection of fractional inches in the boards inscribed in the circle. When 

 all boards are read to the nearest full inch in width, dropping all frac- 

 tions, some diagrams will lose a much larger per cent than others — while 

 in actual sawing, these variations tend to even up. 



For circles of the same diameter and with the same minimum width 

 of board and saw kerf, the board-foot contents wiU evidently vary con- 

 siderably according to the treatment of these four factors in construction 

 of the diagram. In a well-constructed consistent set of diagrams, the 

 values in board feet should increase by a regular progression. This 

 can be shown by plotting the original quantities on cross-section paper 

 and connecting the consecutive points by straight lines. Irregularities 

 are revealed by sharp angles in this continuous line. Most diagram 

 log rules show considerable irregularity, which the authors made no 

 attempt to smooth out, as could have been done by means of this graphic 

 plotting. A wholly inexcusable variation of such rules is caused by 

 increasing the average width of slab allowed on large logs. This increase 

 does not conform to the actual practice in sawing and results in a larger 

 over-run on large logs. It is the principal defect in both the Scribner 

 and the Spaulding diagram log rules. The Maine or Holland rule, 

 by avoiding this error, secured a more consistent result. 



Diagram log rules tend to give the scale of perfect logs under a given standard 

 for saw kerf and width of slab. The waste for normal crook and irregular form 

 cannot be shown. Since the commercial rules have ordinarily allowed too thick a 

 slab or too wide a minimum board or have rejected fractions, this loss is compen- 

 sated, but formula rules if accurate are more practical and convenient. 



Baughnan Log Rules. As an example of a diagram rule which is too perfect 

 for commercial use, since it neglects shrinkage and normal crook and includes frac- 



