282 



THE MEASUREMENT OF STANDING TREES 



The eye must be on a level with the stick (assuming that the tree 

 is erect). 



The eye must be at the proper distance from the tree. 



The stick must be held horizontal (assuming again that the tree 

 is erect). 



The stick must be held perpendicular to the line of sight from the 

 eye to the center of the tree at the point of measurement. 



Errors of 1 per cent in the measurement of diameter are incurred 

 under the following conditions: 



The figures given represent the distances by which the position 

 of stick or eye departs from the above conditions. 



TABLE XXXVIII 



Errors in Using Biltmore Stick * 



Sign 



Resulting in Error of 

 1 Per Cent in Diameter 



D.B.H. of trees 



60 

 Inches 



+ 



+ 



± 

 Usually 



Eye above or below stick by 



Stick not horizontal — one end higher than 



other by 



Stick not perpendicular to line of sight — one 



end nearer the eye than the other by 



Eye too near to or too far from tree by. . . . 



Measurement at wrong height 



Tree irregular in shape 



7.1 



4.1 



5.1 

 0.45 



(Variable) 



(Very variable — consider- 

 ably greater than with 

 calipers) 



* Donald Bruce, Proo. Soo. Am. Foresters, Vol. IX, 1914, p. 46. 



A still more serious error is incurred through the inevitable tendency of the 

 cruiser to raise the stick to the level of the eye, rather than lower the eye to the 

 level of the stick. If the stick is held at 4£ feet and the eye remains at 5 feet 

 3 inches, with a difference of 7 inches in height, the error is but 1 per cent of the 

 diameter, but if the stick is raised to the level of the eye, the diameter at the point 

 measured is appreciably less than D.B.H. The resultant average error varies from 

 3 to 6 per cent, dependent upon the rapidity of taper, and increases consequently with 

 the diameter of the 1 tree. 



The following table gives the graduations which should be placed upon Biltmore 

 sticks for a reach of from 23 to 27 inches respectively: 



