80 CIRCULAR. 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



5. If the diameter tape is used in place of the calipers a special investigation 

 should be made to determine the average difference between the measure- 

 ments by the two instruments for the species in question. 



6. Total height should be measured from the average ground level to the 

 tip of the leader. 



7. Height should be recorded to the nearest one-half foot. 



8. If possible, height should be measured by tape or measuring stick before 

 the tree is divided into sections. If not, it should be obtained by summing 

 the lengths of the individual logs plus those of the stump and the tip. 



9. Height should be measured with tape or measuring stick. 



10. Merchantable height should be taken to a fixed diameter limit; 5 inches 

 if the International rule is to be used, and either 6 or 8 inches, according to 

 local standards of utilization, if the Scribner rule is to be used. 



11. Age should be determined by stump counts on 10 to 25 percent of the 

 trees, selecting trees of varied sizes. 



12. Diameters should be measured at regular intervals up the tree as 

 follows : 



(a) At 8.15-foot intervals where maximum height of timber does not 

 exceed five logs; 



(5) At 16.3-foot intervals for taller timber. 



13. The height of stump should be 1 foot in the case of second-growth and 

 1% feet in the case of virgin timber. 



14. The following intermediate taper measurements should be taken near 

 the butt of the tree: 



1 foot above stump. 



2 feet above stump. 

 6 feet above stump. 

 8.15 feet above stump. 

 12 feet above stump. 



(Except in the case of trees which are irregular in form at these 

 points on account of fire scars, turpentining, etc.) 



15. Diameters up the tree should be taken at lengths which are measured 

 from the standard stump height (see no. 13) instead of from the actual 

 stump height. 



16. All diameter measurements should be taken by means of calipers, and 

 should be the average of two measurements at right angles, to the nearest 

 one-tenth inch. If diameter tape is used, an investigation should be made 

 of the average difference between measurements by the two instruments. 



17. The average bark thickness should be obtained at each point of diam- 

 eter measurement to the nearest five one-hundredths of an inch by averaging two 

 measurements made at points diametrically opposite each other. 



18. The standard instrument for obtaining bark thickness is the Swedish 

 bark-measuring instrument. 



19. The following characteristics should be considered as making a tree 

 too abnormal for use in volume tables : Forked tops, broken tops, a heavy 

 lean, and turpentining or fire scars which distort the d.b.h. measurement. 

 Tops repeatedly broken back by whipping should not disqualify trees of species 

 for which this is a normal condition. 



OFFICE COMPrTATIOX 



20. In computing cubic-foot volume the stump should be considered a cylinder, 

 with a basal area corresponding to the diameter at stump height. 



21. Logs should be cubed by the Smalian formula, using short sections as 

 indicated by no. 13 for butt log and 8.15- or 16.3-foot sections, as indicated in 

 12 (a and b) , for the remaining logs. 



22. The tip should be cubed as a paraboloid. 



23. The computations may be performed by using multiple basal-area tables, 

 alinement charts, or the basal-area slide rule. 



24. In cubing, three significant figures should be retained. 



25. The values for the fundamental table should include stump and tip but 

 no bark, while subordinate tables may be prepared for merchantable volume, 

 exclusive of stump or tip and inclusive or exclusive of bark (no. 35). 



26. In computing volume board measure the standard log rule for second 

 growth is the International %-inch kerf. In addition, where the timber is 

 already merchantable the local rule may in some instances be used. 



