440 ESTIMATION OF INCREMENT 



This formula gives a rate of compound interest very 

 slightly lower than the true rate of compound interest. 



It will readily be seen that where data are available, this 

 formula is applicable for general purposes, whether a per- 

 centage increase in cubic feet or in money value is being 

 considered ; and, whether it is the percentage that has occurred 

 in the past or will occur in the future. 



For general purposes the formula might be expressed 

 thus : 



_ 200 Increment 



n Contents or value now 



+ contents or value at period of n years 



In the example given above the rate of interest that took 

 place during the last 10 years is given ; but, speaking generally, 

 it will be found that it is of far more importance to be able to 

 gauge the probable rate of interest that is likely to take place 

 in the future, or is taking place at the present moment. 



In this connection it is necessary to have regard to the 

 fact, that, in crops of normal density, any change in the rate 

 of height growth, or of the width of the annual rings for a 

 short period of years, is nearly always very gradual, and when 

 once the principal height growth has been attained the total 

 increment per acre, from year to year, or from one short 

 period to another, does not usually vary suddenly. Hence, the 

 increment that may be expected in the immediate future may 

 be considered as about the same as that which has just accrued. 

 Perhaps a little more, or a little less, according to the vigour 

 and density of the crop, and as other circumstances shall dictate. 



But the rate per cent, that will be yielded will not usually 

 be so high, for the increment has to be reckoned as a per- 

 centage on a much greater capital. 



When, however, investigating the rate of growth of crops, 

 it will not usually be found that any accurate measurements 

 of that crop have been previously taken ; hence, it will often 

 be necessary to gauge the increment of the crop without 

 previous measurements for comparison. 



This may be done by finding the increment on average 

 sample trees, and then calculating the increment per acre. 



