Many illustrations in this book, taken from pubhcations of excellent standing, show dates (such as years, months, etc.) at the top of the chart. If the horizontal scale were always placed at the bottom, the standard arrangement would be a convenience to the reader and would give the additional advantage that the top of the

CURVE PLOTTING

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chart would be free for a numerical statement such as is found at the top of Fig. 68.

The scales of any curve chart should be so selected that the chart will not be exaggerated in either the horizontal or the vertical direction. It is possible to cause a visual exaggeration of data by carelessly or intentionally selecting a scale which unduly stretches the chart in either the horizontal or the vertical direction. Just as the English language can be used to exaggerate to the ear, so charts can exaggerate to the eye.

A curve permits of finer "^Ssliisil

interpretation than any other known method of presenting figures for analysis. Fig. 69 gives some information which many persons might not fully grasp if only a column of figures were used to indicate the average yearly earnings of Princeton graduates. The fairly uniform slope of the curve for the first six years after graduation indicates that the men were receiving almost uniform raises in pay each year. It must be remembered that a straight-line curve simply indicates that the amounts of the increases year by year are uniform in numerical value. If a curve were started at the lower left-hand corner of the chart and drawn diagonally across each of the rectangles of the chart, it would be seen at once that there would be a straight line indicating an increase in salary of $500 per year.