A chart of this kind would be especially striking if used in advertising, or in a report where concentration upon only one general idea was needed, without a great amount of specific detail. Though Fig. 116 shows that telephone rates have had a constantly downward

GRAPHIC METHODS

je99 1900 1901

I90a (905 1906 1907 (908 (909

Courtesy of Daia, Cfiicago

Fig. ii6. Chicago Telephone Rates per Year Compared with the Nvunber of Telephones in Use in Chicago

It is the object in this chart to show that the rates have been consistently reduced as the number of telephones has increased. The curves shown earlier in this chapter have varied directly, usually going up or down simultaneously. Here we have an inverse relation, with one curve coming down as the other goes up

trend as the number of telephones in use has increased, there is, after all, no real proof in the chart that the rates have decreased in proportion to the increase in the number of telephones in use. Fig. 116 stimulates interest and makes one wish to plot another

chart in which the number of telephones in use would be the horizontal scale and the average rate paid would be the vertical scale, somewhat on the general scheme of Fig. 119. The plotted points for different years on a chart of the kind suggested would show by the arrangement of the points whether the prices had changed exactly in accordance with the number of telephones in use.

Fig. 117 has been very carelessly drawn in that the two curves do not have their vertical scales start at the same zero line. The zeros for each of these scales are so close to the curves as drawn that it would have been a very simple matter to have made one zero line for both scales at the bottom line of the chart itself.