A time chart like Fig. 60 can often be used advantageously in conjunction with other time charts covering the same period of time. Thus, in studying tug-boats, the information on a chart for lighter operation such as is shown in Fig. 59, and on charts for the operation of car-floats or of float bridges, may be valuable. All the various kinds of equipment with which the tug-boats may be employed could be considered in the study, if it is to be determined whether or not the most effective use is being made of the tug-boats. If all the charts used in the study are drawn to the same horizontal scale, the charts can be placed immediately above each other so that the operations of all related equipment for every hour of the day and night can be instantly seen during the whole of a test period, of, say, a week or a month.

The charts thus far considered in this chapter have shown time in the horizontal direction only. In Fig. 61 we have time shown by days in the horizontal direction and by hours in the vertical direction. This type of chart is extremely valuable in determining whether or not schedules are maintained uniformly over any period of time.

CO GRAPHIC METHODS

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.