Difficulties and Errors in Stem Analysis. 15 



a. Find an available radius as nearly equal to the average 

 radius as possible ; count off the decades on this. 



b. Draw a line from the pith, at 90° or less from the radius on 

 which the decades were counted, make it the length of the 

 average ladius. 



c. Connect the ends of these two lines already drawn by a ' 

 third. Lines drawn parallel to this third line from the decades 

 marked off on the radius will cut the real radius giving the re- 

 quired decade lengths. The lines are easily drawn parallel by 

 means of the rule and a tally sheet for a triangle. 



In determining the width and age of the sap wood, a very im- 

 portant measurement in some species, it will be found that the 

 average radius seldom crosses the sap at its average width. It is 

 necessary, therefore, that the width of sap appearing on that radius 

 be disregarded, and the average width be laid off at the end of the 

 average radius ; the number of rings to be found in the space 

 thus laid off Vv'ill give the true age of sap wood. 



The first operation in the series of form measurements is to 

 measure the height of the stump. This is necessary for two 

 reasons ; first, that the full volume may be calculated ; secondly, 

 that the " breast high " point on the butt log may be properly 

 located. 



Stumps are measured in height to the nearest half foot ; this 

 operation would, therefore, at first sight seem simple, yet trees 

 do not grow regularly, as one would wish ; they grow on side 

 hills, on boulders, on logs, against one another. Three out of 

 four times there is no trouble in " declaring " a stump, but the 

 third time one might throw it into one class or another. The 

 error here involved might appear to be compensating ; it is not ; 

 involving the personal equation it is accumulating. One man 

 will invariably throw the doubtful stump in the upper height 

 class, another man would throw it in the lower. 



The following typical example will show the result of the 

 error involved. 



A stump whose diameter is 41.4" was called two and a half feet 

 high instead of two feet ; by so doing it was credited with a larger 

 volume than it really possessed ; by calling the stump a half foot 

 higher than it really was, the breast high point was lowered one 

 half a foot on the log, thus occasioning a change in the breast 



