Errors in Bstimating Timber. 



175 



timber on the area for sale, an accurate cruise becomes of con- 

 siderable importance. To discover how serious a change in the 

 stumpage price would be made by an error in estimating, two 

 bodies of timber, one in the Yosemite and the other on the Plumas, 

 each containing approximately 300,000,000 feet, were appraised 

 and then reappraised after changing the timber estimate by 5 and 

 then by 10 per cent. It was discovered that an error of 5 per 

 cent, in the estimate would make a difference of approximately 

 8 cents per M feet in the case of the Yosemite timber, where the 

 appraised stumpage was $3.15 per M. and about 7 cents in the 

 case of the Plumas, where the appraised value was $2.37. An 

 error of 10 per cent, in the estimate will make a differenc of 

 about 20 cents per M. feet in either case. Figuring an average 

 cut of 20,000 board feet per acre, this error means a loss per 

 acre of $1.40 if the error is 5 per cent, and $4.00 if the error is 

 10 per cent., either to the Government, if the cruise is an under- 

 estimate, or to the operator if the cruise is' an overestimate. This 

 expressed in terms of per cent, of stumpage price means that an 

 error of 5 per cent, in the estimate will affect the price by 2^ 

 per cent, and an error of 10 per cent, will affect it by 7.2 per cent. 



Cruisers estimating timber for private purchasers or sellers 

 as a rule aim to get the estimate within 10 per cent. In other 

 words, a cruiser's work is passable if he comes within 10 per 

 cent, of the actual timber on the tract. Providing his cruising 

 is uniform this would mean an error of 10 per cent, in the 

 value of the timber on the area. It appears advisable, there- 

 fore, to spend a little more money in order to get a more ac- 

 curate cruise. 



The following deductions may be safely made from the above 

 discussion and tables : 



Assuming that the method of estimating is correct and it is 

 carefully applied, a 5 per cent, estimate will give fairly satisfac- 

 tory results for an area not less than about 1,500 acres. A 10 

 per cent, estimate may give fairly satisfactory results for an 

 area as small as a section in extent, but for smaller areas than 

 that even a 10 per cent, cruise is not very reliable. Where more 

 detailed estimates are desired more intensive cruises are essen- 

 tial. The practice of making a 5 per cent, or even a 10 per 

 cent, cruise and then giving out the estimate by 40 acre units is 



