INFLUENCES AFFECTING OVER-RUN 47 



were intended, of measuring in the log the possible output of lumber. The sawed 

 product tends to over-run the scale of contents shown by the log rule. 



An excess of sawed over scaled contents of logs is termed the over-run. 

 The over-run is always stated as a per cent of the log scale. The log 

 rule, whether accurate or defective, is accepted as the fixed standard, 

 giving the same contents for all straight and sound logs of the same 

 dimensions. Over-run, on the contrary, will vary with several factors. 

 A knowledge of the average per cent of over-run which may be expected 

 over the scale enables both buyer and seller of logs to gage their value 

 more accurately. As value is dependent on the price of lumber, the 

 dealer in logs must know whether for every 1000 board feet of lumber 

 scaled by the log rule, there will be obtained say 1250 board feet of 

 sawed lumber, or only the 1000 board feet scaled, for in the former 

 case the logs are worth 25 per cent more per 1000 board feet of scaled 

 contents than in the latter. 



47. Influences Affecting Over-run. The Log Rule Itself. Two log 

 rules giving different scaled contents for logs of the same sizes will yield 

 correspondingly different per cents of over-run. Each rule is arbitrarily 

 assumed to represent a standard of 100 per cent, the over-run being 

 computed in terms of the rule employed. 



For instance, a given quantity of logs when scaled by the Doyle rule may measure 

 67,000, and saw out 100,000 board feet. Instead of stating that the log scale gives 

 67 per cent of the actual product, with an "over-run" of 33 per cent, the scale is 

 taken as the standard or 100 per cent, and the correct over-run in this case is 49 per 

 cent. When scaled by the Scribner rule, these same logs may give 85,000 board 

 feet. In this case the over-run will be 17.6 per cent since 15,000 board feet is 

 17.6 per cent of 85,000 board feet scaled in the log. 



Since the quantity of sound lumber contained in logs can be measured with 

 only approximate accuracy, due to hidden defects and other factors, the buyer 

 demands a certain margin of safety. A reasonable over-run of from 5 to 10 per 

 cent is usually expected. With a properly constructed log rule, the over-run should 

 be about the same for large as for small logs. The worst defect which a log rule 

 can possess is inconsistency in scale between logs of different sizes (§39). Slight 

 irregularities in scale of individual diameter classes may average out in the general 

 run of logs. But when the per cent of board-foot contents scaled by a log rule 

 increases or decreases in proportion to size of log, there is no way of adjusting it. 

 The over-run will then vary with the average size of the logs scaled. Such a rule 

 can never give permanent satisfaction to both the buyer and the seller of logs. 



48. Influences Affecting Over-run. Methods of Manufacture. 



With a fixed standard set by a log rule, the greater the economy of man- 

 ufacture, the greater will be the over-run. Any factor which reduces 

 the waste in manufacture increases the output. The waste in straight, 

 sound logs consists of slabs, edgings, trimmings and sawdust. In addi- 

 tion, there may be a loss or gain in the scale of lumber due to fractional 

 thicknesses not measured in board feet (§ 20). 



