Though it is fairly easy to see in Fig. 128 what the changes are which have occurred in, say, the item for "General" expenses, it is not at all easy to determine the changes which have occurred in the item for "Conducting Transportation." The eye cannot measure correctly the increase or decrease in width of any area as great as that representing the item for "Conducting Transportation," especially if there is no straight line to gauge by, either at the top or the bottom of the area under consideration.

Though the method of presenting the facts in Fig. 128 is excellent to give a rough general idea or to reach unskilled readers, the method of presenting the facts in Fig. 129 is likely to give the more accurate impression. In Fig. 129, each of the different expense accounts is

GRAPHIC METHODS

Percent

plotted as a separate curve measured from zero as a base line. It can be seen at once in Fig. 129 that the component for "Conducting Transportation" increased rapidly until 1895, ran along fairly uniformly to 1900, then slightly decreased, then increased again. By having each curve plotted separately with the points measured from a zero base line, the eye can judge instantly and accurately the changes which have occurred over a period of years in any component which enters into the total. In an illustration like Fig. 129 it should be

shown in the title, or preferably on the chart itself, that the sum of the heights of all the curves given on the chart is constantly 100 per cent as indicated by the broad line at the top of the chart. The reader will then know that if any one curve on the chart goes up, some other curve or curves must come down in order that the 100 per cent line may remain straight and horizontal.