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.

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Adapted from Railway Age Gazette

Fig. 128. Percentage Distribution of the Expenses of Operating the Raihoads of the United States

Here a number of different factors enter into the total 100 per cent. Since the strips representing different expenses vary at both top and bottom, it is not easy to see from year to j'ear how much any strip may be increasing or decreasing. Compare with Fig. 129

Fig. 130 is an interesting application of the method of using areas to show components with 100 per cent shown as a straight line at the top of the combined area. As in this case a large part of the construction work was finished, the actual number of accidents in the construction department dropped to almost nothing, and, because the shaded area for construction grew less, it was necessary that the other areas should widen out if the 100 per cent line at the top were to remain a straight line. Here the weak point in the method of charting is the same as that indicated for Fig. 128. The person observing the chart has no way of telling whether the factors included in the 100 per cent have grown less or grown greater, and whether