If the curve of Fig. 76 were plotted on the same horizontal scale as the curve of Fig. 77, the flood would appear to be much more severe and rapid than it appears from Fig. 76.

CURVE PLOTTING

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Atob/7 /Voon Noon

Sept.eth Sept.Tth. Sept.ath.

Time in Hours

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

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

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 ^ 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 particerror made by persons

ZDOOO 24 25 26 27 28 29 JO jr I 2

March. 1913 April

Engineering Retard

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