Page:Graphic methods for presenting facts (1914).djvu/121

 Where charts for index numbers are made on the 100 per cent basis, it would seem best to have a broad line for the 100 per cent line. If there is not room to extend the co-ordinate field down to the zero of the vertical scale, the co-ordinate field may be shown broken off with a wavy line at the base indicating to the reader that the bottom of the chart is not a zero line, and that the chart must be read on the 100 per cent basis.

Fig. 93. Fluctuation in the Price of Eggs in the United States as Compared with the Average of the Monthly Figures for the Preceding Four Years

The Government Crop Reporter is intended to be of service to farmers. Any charts included should be as clear as it is possible to make them. The illustration above is submitted only as a suggestion

Fig. 93 was drawn from the data of Fig. 92 as a suggestion for a type of chart which might be used where an untrained class of readers must be reached. By plotting increases above the zero line and decreases below the zero line, a chart is obtained which needs little space and which nevertheless is on a large scale, giving a great amount of detail so as to permit accurate reading of all the various points on the curve. There is very small chance for any untrained reader to misinterpret a chart made by the general method used in Fig. 93.

Fig. 94 is essentially a chart relating to index numbers. The vertical scale, instead of being shown with 100 per cent to represent unity, has zero placed opposite the line representing unity. The chart does not clearly point out that the curve drawn above the zero or unity line represents increases in revenues and not total revenues. A much greater fault with the chart, however, is found in the fact that the chart compares the operation of a railroad in different years by using the year 1908 as unity. 1908 was a panic year, with very serious business depression affecting railroads even more than some