Page:Graphic methods for presenting facts (1914).djvu/99

 In general, it is unwise to compare the shapes of two curves unless they are plotted to the same scales, both horizontal and vertical.

Engineering Record

Fig. 76. Curve Showing Duration of a Flood, September 16, 1909, in the Canadian River, New Mexico

This curve was first plotted on a paper having co-ordinate lines close together. For ease of reading, the intermediate lines were omitted from the magazine illustration

The curve of Fig. 77 is misleading because the scale does not begin at zero. Only the peak of the flood is shown, with no zero line from which to judge the extent by which the flood exceeded the normal flow of the river. If the co-ordinate lines were drawn so as to show the zero line, the base of the chart would be about 3/8 inch lower than it appears in Fig. 77, and the whole curve would make a different impression. The omission of the zero line in charts of this kind is particularly irritating, yet it is a very common error made by persons drawing charts.

Engineering Record

Fig. 77. Flood in the Hudson River at Mechanicsville, N. Y., March, 1913

Note the different scales at the right and the left by which the curve may be interpreted. This chart is misleading because the scales do not begin at zero

Note that in Fig. 77 the curve can be read from two distinct scales, one scale on the left side of the chart, and a different scale on the