Graphic Methods for Presenting Facts
This similarity in shape shows conclusively how much the reader would be misled if he should assume that the increasing slope of the curve in Fig. 120 proved in itself an increase in the rate of growth. The actual percentage rate of the growth for Fig. 120 can best be studied by making an entirely new chart for the purpose of observing percentage rates only.
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pound Interest for Thirty-six Years
Here the rate of increase is uniformly 10 per cent per year, but the slope of the curve is constantly changing. The general shape of this curve is somewhat similar to the shape of the population curve for the United States seen in Fig. 120. The slope of a curve plotted on ordinary coordinate paper tells nothing about the percentage rate of growth. See Fig. 122 and Fig.
132 GRAPHIC METHODS
* The ordinary form of graphic chart plotted on rectangular coordinate paper with the natural or arithmetical spacing of the lines has some serious limitations which may cause a chart to be misleading. The true function of such a chart is to portray comparative fluctuations. This desired result is secured clearly and satisfactorily when the factors or quantities compared are of nearly the same value or volume, but analysis will show that the result is not accomplished when the amounts compared differ greatly in value or volume. The extent or degree of the fluctuation as indicated on the ordinary chart depends in a measure on the proximity of the curves to the top or bottom of the chart.