THE CONTENTS OF LOGS AND TREES 173 



It will vary with many factors, such as the thickness of the 

 saw, the efficiency of the machinery, the skill of the sawyer, 

 the thickness of the boards sawed, the defects in the logs and 

 others. This will account in some measure for the many rules 

 in existence. 



Log rules are constructed in several ways, some by math- 

 ematical formulae some by diagrams of the small ends of logs, 

 some are based on actual experience at the mill in sawing 

 boards from logs, and others by correcting existing log rules 

 to fit local conditions. 



The following log rules are in most general use in the 

 eastern part of the country: 



The Scribner Rule. The Scribner rule was constructed 

 by the use of diagrams. It is the oldest rule in general use. 

 Circles were drawn the size of the small ends of logs of dif- 

 ferent diameters and in these circles the inch boards that 

 could be sawed from them after allowing for waste in sawing 

 were mapped out. From these the number of board feet 

 that could be sawed from logs of different lengths were found. 

 The results for logs of different diameters and lengths were 

 then arranged in a form of a log table. 



A modification of this rule, called the Scribner Decimal 

 Rule, has been made by dropping the unit figures and round- 

 ing the values to the nearest tens. This is the log rule adopted 

 by the United States Forest Service for timber sales on the 

 National Forests. The Scribner Rule is said to give very 

 fair results for logs below 28 inches in diameter, but for logs 

 above the results are too low. 



The Doyle Rule. The Doyle Rule is based on the follow- 

 ing mathematical formula: Deduct 4 inches from the diam- 

 eter of the log inside the bark to allow for slab, square one- 

 quarter of the remainder and multiply this result by the length 

 of the log in feet. This rule gives very low results for small 

 logs, and above 36 inches in diameter the values given are too 

 large. This is because the width of the slab removed by the 



