AVERAGE DIAMETER GROWTH FROM ORIGINAL DATA 347 



read directly in diameter growth. From this curve, the growth at 

 10, 20, 30 years, etc., is then read for the table. 



o - 



o 



Radius, Inches 



(Double to read Diameter) 



Fig. 69. — Growth in radius of 5 spruce trees plotted separately, and curve of average 

 growth. The average number of years in first fractional decade is 7. The 

 successive decade averages are plotted on 17, 27, etc. The last three points 

 represent averages based on less than five trees and should not be plotted on 

 the same curve. 



The growth of each tree is shown by curves. In plotting data for a 

 growth curve the points plotted for single trees would not ordinarily be con- 

 nected. The average would either be sketched by eye, or plotted from the 

 position of the average points as indicated. 



Substitution of Graphic for Arithmetical Method. For this computation 

 graphic plotting of the original data is sometimes substituted. This method is also 



