Page:Graphic methods for presenting facts (1914).djvu/276

 *sult is very confusing on account of the fact that the vertical lines connecting the flat tops may coincide. When one line falls directly on top of the other, there is no way for the reader to judge which curve is which beyond the point of intersection. Unless the curves are very carefully colored or dotted there is great danger that the reader will jump from one curve to the other in his interpretation of curves which happen to meet. This weak point in the flat-top method is particularly noticeable if blue prints must be made from original charts in which the flat-top method is used. On the original chart the curves can be fairly well distinguished by using different colored inks, but as the colors are lost in blue-printing, each blue print must be colored by hand, using the original chart as a key to show what the colors should be. If a peak-top method of plotting is used, numerous curves may be run across the same sheet and yet be distinct enough for identification even when all are reduced to uniform white lines on the blue print. It would be easy to name fifteen reasons why the method of plotting with peak tops is superior to the method of plotting with flat tops. The advantages of the peak-top method seem so obvious that it is believed the reader will agree to its desirability, without further argument being given here.

Courtesy of Factory

Fig. 203. Lubrication Cost per Ton of Product for a Factory in the Year 1908

The figures at the top of the co-ordinate ruling give the data from which the curve was plotted. Though data should be put on all charts, figures arranged in the direction here shown are not in convenient form for addition. See the later illustrations in this chapter for methods of placing figures above each point on a curve

The man who plots a curve has before him the data showing the actual value for each point plotted on the curve. If any questions arise in his mind regarding the comparative figures at different points on the curve, he can refer to the data from which the curve was plotted.