METHOD OF MILL RUN APPLIED TO THE STAND 299 



of knots, while trees grown in dense stands have a higher per cent of 

 upper grades due to the history of their development. The skill required 

 in judging the per cent of grades in standing timber is based directly 

 on these two sources of information and is not a matter of guess work. 



232. Method of Mill Run Applied to the Stand. Data on grades 

 produced in sawing takes two forms; the total output by grades for 

 mills sawing in a given region and character of timber, and the specific 

 contents of logs of different sizes and quality, as determined by mill- 

 scale studies (§ 361, Appendix A). This corresponds with two dif- 

 ferent methods of applying the information on grades to the standing 

 timber, namely, application to the stand as a unit, and application 

 to the tree or log units. 



In applying mill-run grade per cents to the stand, the total estimate 

 in board feet is arbitrarily divided into the different grades which it 

 will probably yield, by per cents of this total. This method corresponds 

 with that of ocular estimate of a stand (§ 206) and its results are about 

 equally unreliable. The basis is the sawed output by grades from mills 

 in the vicinity. These per cents so obtained will apply to the timber 

 in question, only if it happens to average the same in quality as that 

 sawed, which assumption, considering the great variation in standing 

 timber, is wholly untrustworthy. This means that the per cents of 

 grade must be modified as the timber is better or poorer than that 

 sawed, which requires a knowledge of the standing timber previous 

 to sawing. 



233. Method of Graded Volume Tables Applied to the Tree. Evi- 

 dently, a better basis is required and, just as in timber estimating for 

 volume, this must be found in the use of the tree unit or the log unit, 

 by which the varying quality of the timber can be standardized. 



The tree unit has not proved a satisfactory basis for grading, though 

 it is possible to use it. The basis is graded volume tables (§ 165) which 

 show the per cent of standard grades in trees of different diameters, 

 preferably in the form of per cents of contents. 



These per cents could be applied to the trees in each diameter class 

 and the total estimate divided in this way into the component grades. 



The objection to this method is that it is not sufficiently elastic 

 to take care of the great range of quality in trees of the same diameters. 

 A given graded table will hold good only for timber of a certain character; 

 if more open-grown, shorter boiled or limbier, or otherwise different, 

 the volume table is not applicable. The method is probably better 

 than the ocular guess, but is equally subject to large corrections in the 

 field. 



234. Method of Graded Log Rules Applied to the Log. The third 

 method employs the log as the basis of grades, and applies this basis 



