THE THEORY AND PRACTICE OP WORKING PLANS 25 



pass, aneroid, note-book, and estimate all at the same time. 

 Either he must make an ocular estimate of the whole stand or 

 else confine himself to quarter-acre (or similar sized) sample 

 areas at definite intervals. Only in cases of need is this sample- 

 area method advised; it is usually better economy to use a 

 two or more man crew. The work goes better, and is more 

 accurate, the men check each other's judgment and, finally, 

 in case of accident, the single man is not left helpless. 



The strips must gridiron the forest. The interval between 

 the grids depends on the purpose of the work. For a reliable 

 estimate 5 to 10 per cent of the area should be covered.* This 

 means: 



For 5 per cent of area: chain- wide strips 20 chains apart. 



For 5 per cent of area: strips two chains wide, 40 chains 

 apart. 



For 5 per cent of area: j-acre sample areas, 2^ chains apart 

 on strips 20 chains apart. 



For 10 per cent of area: chain-wide strips 10 chains apart. 



For 10 per cent of area: strips two chains wide 20 chains apart. 



For 10 per cent of area: |-acre sample areas, 2^ chains apart 

 on strips 10 chains apart. 



A very practical way of recording the estimates is by 2 or 

 3 inch diameter classes, beginning with the smallest merchant- 

 able diameter, supposing this to be 11 inches, as follows: 



* Margolin in an article on " Errors in Estimating Timber," For. Quart., Vol. 

 XII, No. 2, pp. 167-176, says: 



" Assuming that the method of estimating is correct and it is carefully applied, 

 a 5 per cent estimate will give fairly satisfactory results for an area not less than 

 about 1500 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 essential. The practice of making 5 per cent or even 

 a 10 per cent cruise and then gi\'ing out the estimate by 40-acre units is inaccurate 

 and misleading and should be discontinued, especially so since such a detailed 

 estimate seldom serves a useful purpose. 



" The greater accuracy obtained by a lo-per cent cruise over a 5 per cent 

 cruise is entirely out of proportion to the difference in the costs, and it appears to 

 be good business, therefore, to make the more intensive cruise, especially where 

 detailed figures are desired." 



