522 Forestry Quarterly 



The more detailed the comparison is made, the wider become the 

 hmits of error. 



If each species is differentiated into three size classes and within 

 each the deviations from the true volume are ascertained, the 

 following limits of error are found : 



Circle method +6.3 percent and —10.5 percent 

 Strip method +11.1 " " " -10.1 " " 



Common square +30.9 " " " -42.2 " " 



These figures show that as regards accuracy there is not much 

 difference between the circle and strip method; but the common 

 square method is liable to great error. This fact is still more 

 strongly brought out by comparing the figures not of the whole 

 series, but of each stand separately. To secure a general measure 

 of accuracy an error limit must be assumed below which the esti- 

 mate will be considered still as sufficiently accurate. If, for in- 

 stance, a deviation of 10 per cent is not to be acceptable, the relative 

 accuracy of the three methods, calling the results of calipering 100, 

 was 100 : 74 : 74 : 55, i. e., out of 100 estimates only 55 times will a 

 satisfactory result be attained by the common square practice, 

 the other two methods satisfying 74 times; or comparing only the 

 three methods with each other, they stand as 100 : 100 : 74. 



The author adds that the stands due to the composition and 

 conditions and great variation furnished a difficult basis for accu- 

 rate estimates. In uniform stands there might not be found any 

 difference with the different methods. It was observed that on 

 gentle slopes all sample area methods work more accurately than 

 on steep slopes. In denser stands, they furnish more accurate 

 results than in opener stands. The circle and strip methods furnish 

 better results than the square method even if the size of the square 

 is considerably increased beyond the customary 1^ acre (1 hectar). 



As regards the time reqtiirement of the different methods, the 

 nimiber of men employed makes a difference, also whether sample 

 trees are felled or volume tables are used, and lastly what per cent 

 of the total area is measured. A table attempts to give results 

 under various assimiptions. 



The interesting conclusion is that the common method, which is 

 the least accurate, is also the most time consuming, no matter 

 whether volume tables are used or sample trees felled; the strip 

 method being most favorable. This relation between the methods 



