Page:Graphic methods for presenting facts (1914).djvu/274



CURVES FOR THE EXECUTIVE

With the exception of the railroads, there are relatively few businesses which make a practice of plotting curves to show operating records in convenient form for the use of executives. Railroad accounting is more highly standardized than accounting in industrial corporation work. The standardized method of accounting has made it rather easy to compare the operating records of different railroad divisions and of different railroad systems. It is probably for this reason that railroads have adopted the use of curves for operating records so much more extensively than have industrial or mercantile businesses.

The upper curve in Fig. 202 is plotted according to the method used on many railroad systems. In this form of plotting a month may be said to be represented in the middle of a space between the vertical lines. Horizontal lines are drawn in the space for each month to a scale representing the figures which it is desired to chart. Lines are then drawn vertically to coincide with the vertical lines of the co-ordinate paper, and they join the horizontal lines of different months in such a way as to give an effect like that of a stairway.

Curves for the same data plotted by the method shown at the bottom of Fig. 202 are much easier to read than those plotted by the step method shown in the upper portion of the illustration. By the method in the lower part of the illustration the plotted line more closely approaches a true curve, there is much less variation in the direction of the lines from month to month, and the general trend of the curve line is easier for the eye to grasp. Compare the two curves for the summer months of the year 1909-10. In the upper curve a series of steps, and in the lower curve an almost straight line from April to September inclusive, indicate an increase by fairly equal increments during those months. Certainly equal increments are more easily represented by the straight