()84 JOURNAL OF FORESTRY 



by simply changing the vakies of the ordinates, so that the curve reads 

 units of diameter growth during ten years for trees of specified diam- 

 eters. It is not necessary to plot the individual points, for with a little 

 practice one can list the two values of each point directly from the 

 analysis sheets and save more than half the time required for the 

 method as just outlined. 



Second. Obtain the number of years required to grow one unit of 

 diameter by taking the reciprocals (rounded off to the closest whole 

 number) of each of the unit values of the above curve. 



Third. Make the simple correlation of diameter breast high inside 

 the bark with the double bark thickness, listing and adding the figures 

 directly from the analysis sheets. 



Fourth. Draw a curve — diameter breast high inside bark based on 

 age. Lay off the horizontal axis in ten-year periods representing age 

 on the stump and the vertical axis, units of diameter breast high inside 

 bark. Begin the curve with a tree units in diameter, plotting the 

 point on the age required to reach the breast-high point (age taken 

 from table of height growth based on age). Then on the ordinate, as 

 many years to the right as are required to cause an increase of one 

 unit in diameter, plot a second point. Plot the third point — two units 

 of diameter — on the number of years required to reach this diameter. 

 Then, above these points, plot the values of the double bark thicknesses 

 (third). Read off the number of years required to reach specified 

 diameters outside bark or rate of growth from the curve drawn through 

 these last points. . 



The method has the advantage of showing the actual accomplishment 

 of trees rather than assuming that growth in the future will be the 

 same as in the past. 



The averages required in Graves' modification of Mlodziansky's 

 method are also handled easily on the adding-machine, either before or 

 after plotting the individual points. 



Another suggestion is that for scientific work volume tables in cubic 

 measure can easily be constructed with relatively few measurements in 

 the field if one uses a cone-form factor and a Dalton adding-machine. 

 The work is similar to that described by Bruce for constructing volume 

 tables by the frustum-form-factor method. The advantage of the cone- 

 form factor is in saving time. The amount of time saved will depend 

 on the sums of the digits in the factors. If the sums run less than 5, 

 the method has an advantage ; but if they are more than 5, there is none. 



There are two types of keyboards on machines that add, those having 

 nine rows of keys and the one having ten keys. 



