30 THE CONSTRUCTION OF VOLUME TABLES 



C. Method of Procedure. 



A. Tabulation 

 1 . Divide a piece of blank note paper into tabular form with the following 

 headings. 



The horizontal lines should be spaced far enough apart to allow the 

 data for all trees included in any 1-inch diameter class to be listed 

 between them in a vertical column . 



Label the spaces successively with the diameter classes they are to 

 represent. 



2. Tally in a vertical column in the space allotted to the D.B.H. measure- 



ments the actual breast high diameters to the nearest 0.1 of an inch, 

 placing each in the space allotted to its class, as determined by the 

 rule that each class shall contain all trees whose diameters ' range 

 from .6 of the one inch to .5 of the next inch higher, inclusive. 



3. In the second column enter opposite each D.B.H. tallied the calculated 



volume of the tree in board feet. 



4. In the third column enter the number of trees in each diameter class. 



5. When all the trees have been tallied, add the actual D.B.H. measure- 



ments in each class, as recorded in the first column, and divide by the 

 total number of trees in the class as recorded in the third column to 

 obtain the average D.B.H., and record it in the fourth column oppo- 

 site its diameter class. 



6. In a similar way add the separate volumes in each class as recorded 



in the second column, and divide by the number of trees in the class 

 to obtain the average volume, and record in the fifth column . 

 B. Plotting. 



7. On a sheet of cross-section paper lay off diameters (D.B.H.) and vol- 



umes as co-ordinates. Determine first which will be abscissa; and 

 which ordinates and be careful to select values for each commensurate 

 with the limits of variation in the data and the size of the cross- 

 section paper. 



8. Plot the average values as determined and recorded in the tables, and 



enter beside each plotted point the number of trees it represents. 



