Fig. 114 shows an error in curve plotting into, which it is very easy for an inexperienced person to slip. One vertical scale is relatively

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P. M Time Monday, Maich 14, 1910 P. M.

Sam. L. NavMaJy, in J<mmal American Society of Mechanical Engineers

Fig. 112. Record of Test of a Steam Turbine of 10,000 Kw. Normal Rating at Plant of City Electric Company, San Francisco, California

The different curves shown in this chart supplement each other so as' to give all the data on one chart in compact form. The scale for each curve given at the left is only sufficient to show the maximum and minimum value for each curve. The zero lines have been omitted entirely. Though charts of this type with numerous curves are sometimes desirable, they must be carefully made or the reader will be misled hy the fluctuations of some one curve appearing more prominently than the data would justify

COMPARISON OF CURVES

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 "cornyield" curve shown in Fig. 114.