Utilization and Accompanying Wastes of One Year's Coal Supply for Locomotives on Railroads of the United States

The double scale permits reading this chart in tons or in dollars

If the chart is made on co-ordinate paper with ruled squares, the reader can obtain the size of each component direct from the co-ordinate lines. The trouble, however, with using co-ordinate paper for charts of this sort is that the components are likely to begin and end at points not falling upon the co-ordinate lines, thus making it necessary to count

GRAPHIC METHODS

fractions of a division at both beginning and end of the component to be measured. The best thing in charts of this kind is to use unruled paper, and specify the scale. The reader, if he wants the exact data, can take his measurements with a ruler. The engineer's scale has its subdivisions in decimals and hence is the most convenient scale for chart work. An engineer's scale should be part of the equipment of every person who has charts to make.

Another method of showing the relative size of the divisions and subdivisions of a unit or group is shown in Fig. 6. In this case we have the total population of the United States split into its component groups according to the condition in regard to marriage. The subdivision bars, given below the total bars, show the conjugal condition in each of the main groups which enter into the total population. Each of these main-group bars is crosshatched to show the conjugal condition within the group. The combined length of the four bottom bars is equal to the length of the total-population bar shown at the top. These same data could have been presented by the method shown in Fig. 5. It will be noted, however, that in Fig. 6 all the figures have been included, and are available for reference purposes without detracting from the utility of the chart itself.