230 



THE MEASUREMENT OF STANDING TREES 



total error of calipers over tape was in the proportion of 21 to 1. The 

 diameter tape should therefore be adopted for all measurements of 

 permanent sample plots. 



.191. The Biltmore Stick. Although calipers can be taken apart 

 for travel and packing, they are cumbersome to carry in timber esti- 

 mating especially through brush and over rough ground. When in 

 addition a beam of 60 inches in length is required, their use becomes 

 extremely burdensome. 



The Biltmore Stick, devised by Dr. C. A. Schenck, substitutes a 

 straight stick for calipers and has been widely adopted by foresters 

 for practical timber cruising. 



The principle of the Biltmore Stick is as follows: A straight stick, 

 if held horizontally, tangent to or in contact with the bole of the tree, 

 and at arm's length from the eye, forms the far side of a triangle whose 

 other two sides are lines of sight from eye to each side of the tree, and 

 which intersect the stick at definite points. When the stick is held 



so that one of 

 these lines of 

 sight intersects 

 one end, a scale 

 can be placed 

 upon the stick 

 starting at zero 

 at this end, and 

 the point of in- 

 tersection of the 

 other line of 

 sight, if the eye 

 is held in its original position without turning the head, will indicate 

 on the scale the diameter of the tree at this point. 



Fig. 42. — Principle upon which the Biltmore stick is 

 constructed. 



Since this intercepted distance on the stick is evidently less than the diameter 

 of the tree, which is at a greater distance and cannot even be seen correctly, the 

 distances corresponding to the diameters wanted will be less than these diameters 

 and this difference increases with diameter of tree, so that the graduations on the 

 stick for successive diameters fall closer together for the larger diameters. The 

 values of the graduations on the stick are directly dependent on the dimensions 

 of the triangle which is determined by the length of the arm or reach. This ranges 

 from 23 to 27 inches with an average of 25 inches. 



The formula for computing the values of this scale is 

 a = length of reach in inches; 

 Z) = D.B.H. 



