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 to make up colored charts by using different colors of drawing ink. The ordinary crayons smear so badly that a chart made with them is sometimes unrecognizable before it is finished.

Fig. 60. Operations of Three Tug-boats in New York for Twenty-four Hours. The Boat Represented by the Lower Bar is in Service for a Twelve-Hour Shift Only

A working chart of this kind would usually be made on a long strip of co-ordinate paper. The illustration was drawn entirely by hand to show the possibilities of hand cross-hatching for bringing out information ordinarily shown in several colors

Fig. 60 is a further elaboration of the method used in Fig. 59. The actual chart from which this illustration was made was drawn on co-ordinate paper ruled in tenths of an inch. Each of these tenth-of-an-inch spaces was made to represent ten-minutes time, so that a much larger scale was obtained than in Fig. 60. As the tug-boat captains regularly kept log-books in which their work was recorded to a five-minute interval the chart was made to the same interval by splitting the ten-minute squares to represent five-minute intervals. With a scale of this size it was feasible to use colored crayons, even though some of the divisions of time were very short.

Fig. 60 was drawn by hand and shows the possibilities in preparing an illustration of this kind when only one color of printing ink is available.

The chart from which Fig. 60 is taken was made to determine how much idle time there was in the operation of three tug-boats, and to ascertain whether the boats could be so run as to reduce the amount of idle time and give better service. The black in Fig. 60 shows the idle time vividly. By looking from bar to bar, it is possible to study all the work of the three tug-boats and to determine whether, if the work were differently assigned, there would be less waiting between jobs. Frequently the tug-boats had to tow two or more lighters or two or more car-floats, simultaneously, as will be seen from the extra