The point on the curve is then placed in the lower portion of the chart at the intersection of the horizontal line representing the number of workers earning a bonus and of the vertical line representing the day, October 10. The curve gives a convenient method of determining the total number of operators who are earning a bonus. When it is desired to know only the number of employees earning bonus each day, the curve shows the matter more clearly than do the black blocks in the upper portion of the chart. The horizontal bars give the story for each worker, the curve gives the total for all the workers.

A chart like that shown in Fig. 59 would ordinarily be made on a long sheet of co-ordinate paper so that the co-ordinate ruling could be used for the vertical lines, indicating time. Co-ordinate paper in several different rulings can be purchased in rolls so that the desired ruling can often be had in continuous lengths. Sometimes, however, the desired ruling can be obtained only in flat sheets of limited size

GRAPHIC METHODS

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TIME CHARTS 57

and it is then necessary to make a long sheet by pasting together several of the separate sheets. The original study from which Fig. 59 was prepared was made upon a built-up sheet seventeen inches wide and eight feet long, so that a full month of lighter operation could be shown on the one chart. ,'