Page:Graphic methods for presenting facts (1914).djvu/127



COMPARISON OF CURVES

There are many men who from long experience have become so skillful that they can glance down a column of figures and obtain quickly a good idea as to the high points and the low points shown by the figures taken as a whole. When it comes to considering two or three columns of figures simultaneously to see whether there is a similarity in the fluctuations shown by the various sets of figures, the number of men who can intelligently grasp the facts presented are rather few. It is in just such problems as these, where a number of different sets of data must be compared, that curves have tremendous advantage over presentation by columns of figures. A man must be almost a genius to grasp quickly the facts contained in several parallel columns of figures, yet anyone of average intelligence can interpret correctly a chart which has been properly made for the presentation of curves. Though there are numerous convenient methods which are useful in comparing curves, we can take up here only the few of those which are likely to be of most frequent use to the average reader.

Fig. 97 brings out the facts of its subject matter with splendid clearness. There are relatively few men who could interpret quickly the data for this chart, if the data were shown to them only as two separate columns of figures. When a chart like that shown in Fig. 97 is used, no mental effort is required to get at the gist of the matter, and the facts can be obtained much more rapidly than would ever be possible by observing columns of figures alone.

A chart like that used in Fig. 97 can be prepared from tabulated figures by any ordinary draftsman in less than one hour of work. The cost of making a line cut is probably no more than the cost of setting the type if the data are to be shown by tabulated figures. The space required for a chart like Fig. 97 is very little