Standard Measures of Accuracy 



Standard measures of accuracy for the three tables are shown in the fol- 

 lowing tabulation: 



Aggregate 



Table deviation Standard error of estimate-^' 



Percent 



Units per acre Percent 



Gross volume 

 Cubic feet 



-0.31 



+890 



+40.8 



Gross volume 



Board foot International +1.79 

 Gross volume 



Board foot Scribner -1.52 



+5,620 

 +4,884 



+54.3 



+52.0 



Tests of the Tables 



A few tests of these ponderosa pine tables were made by comparing plot 



volumes with those obtained from field measurements and with those read from 



composite aerial tables published in Research Paper 41. For the most part, 



these plot series tests showed that mean per acre board-foot and cubic-foot 

 volumes obtained from the ponderosa pine tables differed significantly from 



those obtained from the composite tables, but did not differ significantly 

 from mean volumes obtained from ground measurements. 



In addition, these tables were used by the five photo interpreters who 

 made aerial estimates of ponderosa pine volumes on cutting compartments of the 

 Boise Basin Experimental Forest, and on sales in the Black Hills National 

 Forest in 1958. Summarized in a recent paper,—' these data clearly indicate 

 that properly trained photo interpreters using these ponderosa pine tables can 

 make excellent aerial estimates throughout much of the ponderosa pine type. 



Z_/ Bruce, D. , and L. H. Reineke. Correlation alinement charts in 

 forest research: a method of solving problems in curvilinear multiple cor- 

 relation. U.S. Dept. Agr. Tech. Bui. 210, 87 pp., illus. 1931. 



4/ Defined as the standard deviation of the difference between paired 

 photo and field plot volumes, expressed in units per acre or as a percent 

 of the average plot volume. The standard error of estimate indicated for 

 these aerial tables is large because 1-acre plots measured on photos were 

 compared with 1/5-acre plots measured on the ground. The true value of 

 these tables is somewhat better than these errors indicate. 



2/ Moessner, Karl E. Estimating timber volume by direct photogrammetric 

 methods. Soc. Amer. Foresters Proc. , pp. 148-151. 1959. 



3 



