TIMBER ESTIMATING. 83 
their class, whether small, medium, or large. When the height ofa 
tree is measured, the diameter also is noted. After these height 
measurements have been made a curve is constructed from which 
a table may be made to show the average height of trees of any 
diameter. This is done in the following way: On a sheet of cross- 
section paper (fig. 3) let the vertical lines represent successive 
diameters at l-inch intervals, and the horizontal lines successive 
heights at 1-foot intervals. Assume, for example, that the follow- 
ing measurements were taken for Loblolly Pine: 
ramneger ai WPCWES 2 iS ee a 10-15) 49) 24 
CSLSTg A, Te Eyes Be eal eg a 2m a a ee oe 75 89 99 101 
Mark on the cross-section paper the point where the vertical 
line running from the diameter point 10 meets the horizontal line 
running from the height point 75. Mark the points of intersec- 
tion for the other diameters and heights in the same way. Then 
draw a regular curve through or as near the points as possible 
in the way shown in fig. 3. The height corresponding to any 
diameter may then be read off from this curve. Thus, to find the 
height of a 16-inch tree, note the point where the vertical line 
running up from the 16-inch point meets the curve; then from this 
point of intersection follow the horizontal line to ascertain the 
height. In the example given the average height of a 16-inch 
tree is 86 feet. 
This method is used to find the contents of sample acres in the 
following way: Make a table of four columns. In the first column 
place the diameters; in the second column the number of treesof _ 
each diameter given in the first column; in the third column the 
average height of trees of each diameter, these average heights being 
obtained from a curve such as has been described; in the fourth 
column the contents of an average tree from a volume table; in 
the fifth column the total contents of all trees of each diameter. 
Then add the fifth column, and the result will be the total con- 
tents of the sample acre. 
