By using different colors of ink a chart of this kind can be made so as to show all related operations without the drawing becoming too complex to read. Fig. 61 has purposely been made simpler than the ordinary chart of this kind to overcome the handicap of being limited to only one color of ink in the reproduction.
Charts in the form of Fig. 61 are valuable in that they show on one sheet all the operations occurring during a given period of time—in this case, twenty-four hours. Some conditions, such as the blizzard of January 7, affect all the deliveries to the different railroads. Study of the chart brings out in contrast conditions which are beyond the control of man and conditions which are the result of carelessness or poor management, which usually crop up first in connection with one railroad, then in connection with another, without being so general as to affect all of the curves, as did the blizzard of January 7.
Fig. 62 shows the possibility of simplification when so many different horizontal curves must be shown that easy reading is impossible. The simplification is made in Fig. 62 by showing only one railroad on each sheet. All the figures for one railroad are shown in curves, placed one above the other. Ordinarily curves like those in Fig. 62 will be nearly parallel, for the time interval required to complete each of the steps of work remains about the same day after day. What Fig. 62 brings out most of all is not so much the time interval between the different steps as the information as to whether each of the different steps was started promptly on schedule. Any one operation started late must delay all the following operations.
The paper on which Fig. 62 was drawn is in itself worthy of attention. This letter-sheet size of paper was carefully laid out so that a typewriter could be used for the lettering on the margins of the four sides of the sheet. The paper was purposely ruled in squares so that any of the common divisions of time might be shown. The possibilities in this direction are:
The days of the month may be used on the short edge of the paper as in Fig. 62.
Fifty-two weeks for one year can be shown by using the long edge of the paper.
Three years by months can be plotted by using the thirty-six squares on the short side of the paper.
One year by months can be shown by using every third line along the short edge of the paper.
