Page:Graphic methods for presenting facts (1914).djvu/143

 larger than the other, and on that account the curves have been made to coincide more closely than they would have done if both scales had the same zero line. In making comparisons of this kind care must be used to have the two scales start from the same zero line, or the person presenting the charts will be open to the unpleasant suspicion of attempting to "fake."

If the reader cares to see how these two curves would contrast if properly plotted, the left-hand scale for "corn yield" can be changed so that the different horizontal lines will be represented by the figures 0, 7, 14, 21, 28, etc. The data for "corn yield" can then be plotted to the new scale, and it will be found that the new curve does not coincide with the "rainfall" curve as closely as does the "corn-*yield" curve shown in Fig. 114. Though there is some similarity in the shape of curves correctly plotted from these data, the similarity is not nearly so exact as Fig. 114 would indicate.

Courtesy of System

Fig. 113. Records of Freight-Train Operation on a Large Eastern Railroad

Here, as in Fig. 112, the zero lines are not given and the reader must watch the left-hand scales carefully to study percentage fluctuation. Comparison between curves cannot be made accurately by judging from the slope or from the total fluctuation of the curves on the page. Percentage increases or decreases for one curve compared with percentage increases or decreases of other curves give the best basis for comparison

Curves well made ordinarily need no embellishment. Anything used for an eyecatcher should apply definitely to the subject matter of the curves. Here the subject is freight-train operation, but the picture shows the interior of a passenger train