Where great fluctuations occur from time to time and many factors enter into the total, it is best to draw charts in the form of Fig. 129 with a common zero line, or in the form of Fig. 131, where each factor has its own separate base line, or in the form of Fig. 132 and Fig. 133, in which the lines on the chart represent actual quantities rather than percentages of an aggregate or total sum.

Note in Fig. 130 and Fig. 131 the 8V^-inch by 11-inch co-ordinate paper on which the ruling is so arranged that the paper may be used for almost any subdivisions of time, such as days, weeks, months, etc., as seen in Figs. 57, 103. 131, 134, and 156.

In Fig. 130 the paper was used for a time-scale of three years by months, the total height of the chart being put at 100 per cent, using fifty out of the fifty-two spaces on the paper. Fifty-two spaces, corresponding to the number of

Fig. 129. Percentage Distribution of the Expenses of Operating the Raihroads of the United States. The Combined Height of All the Curves Shown Equals 100 Per Cent on the Scale

This illustration represents the same data as Fig. 128. Here the percentage for each expense is read from the zero base line instead of from one to the other of the fluctuating lines on either side of an area. This method, though not so popular as the method of Fig. 128, pennits more accurate reading