In making up charts like that shown in Fig. 59, the data are usually recorded on the chart day by day as reports come in. This involves a large amount of handling of the chart, and the chart is likely to be much smeared by the time the last reports are entered. If colored crayons with the color embodied in paraffin are used, very brilliant colors can be obtained, yet rubbing with the hands will not smear the colored areas. Unless a non-smearing crayon is used, it is better

GRAPHIC METHODS

■■ Idle W^ Towing Carfloat ^^ towns lighter ^g running ught HBtaking Water ^^Coauns

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

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 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 tenthof-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.