QUALITY OF WOODS. 271 



d. Reduction to One Quality. 



Several methods of regulating the yield demand a reduction 

 of the areas of the several woods, or working sections, to one 

 quality, so as to have to calculate only with areas of equal 

 yield capacity. 



Such a reduction to one quality may be made as regards the 

 locality, or the growing wood ; in each case as regards the 

 normal or real quality. The method of procedure is the same 

 in each case. 



The calculation becomes most simple ; either if yield tables 

 are used, in which the yields of the several classes are indicated 

 the best by 1 and the others in decimals of 1 ; or, if the 

 reduction is made with the final mean annual increment or 

 yield. 



Again, the reduction can be made under one of the two 

 following conditions : Either the total of the several reduced 

 areas shall be equal to the actual area of the working section ; 

 in other words, the calculation is made with the mean quality 

 of the area ; or, the above equality is not required, in which 

 case any quality can be used as the standard, frequently 

 that being chosen which exists over the greater part of the 

 area, 



i. REDUCTION BASED UPON THE FINAL MEAN ANNUAL INCREMENT. 



(a) Calculation with the Mean Quality. Under mean quality 

 is understood that which, if it existed throughout the working 

 section, would produce the same total yield as that produced 

 by the several existing qualities in different parts of the 

 working section. 



Let a ly a 2 , a s ... be the several areas, 

 >, y\> 2/2? 2/3 the corresponding annual yields per unit 



of area, 

 ,, Y the mean yield per unit of area, then 



