262 ESTIMATION OF STANDING TIMBER 



Both the degree of accuracy obtained and the expense of estimating 

 the timber are reduced: 



By the reduction of the per cent of area covered. 



By substituting tree counts for measurements of dimensions and 

 averages for totals. 



By substituting ocular measurements of dimensions for instru- 

 mental measurements. 



By substituting pacing for chained or measured distances. 



As an offset to the loss of absolute accuracy by the substitution of 

 these laws of averages and reduction of detail, the relative accuracy 

 or efficiency of the application of the cheaper methods can be enormously 

 increased by the development of technical skill, experience and judg- 

 ment, so much so that the old-time timber cruiser depended upon these 

 factors both for his reputation and the reliability of his estimates. 

 This relative accuracy is increased: 



By the choice of methods and care in location by which partial 

 areas are secured in such a manner as to insure the highest probability 

 of average volumes. This is similar to the methods used in sampling 

 ore. 



By the development of skill and accuracy in the use of pacing 

 and in the use of the eye for measuring diameters, heights and width 

 of strips or plots. 



By the ability to apply the methods of tallying a fixed per cent of 

 the stands or selecting average trees in such a manner that the true 

 average volume of the total number or count is obtained. 



By painstaking observance of obtainable standards of accuracy in 

 the use of instruments for measuring distances, diameters and heights, 

 and in proper record or tally. 



By individual training and ability to make the proper discounts 

 for defects. 



By the careful checking of the reliability of volume tables used, 

 and the correlation of field methods with the conditions for which they 

 were constructed. 



Finally, by correlating all of the above factors with the actual con- 

 ditions of the tract or stand to be estimated, which in themselves will 

 determined the degree of accuracy required in each step as above 

 outlined. 



211. Relation between Size of Area Units and Per Cent of Area to 

 be Estimated. There are two elements to l)e considered in arriving 

 at accurate averages in estimating a given tract. First, the problem 

 of distributing the samples throughout the area in order to obtain the 

 greatest probability of true average; second, the uniformity of the stand 



