may earn a bonus by completing a certain quantity of work each day. It will be seen at a glance that the chart becomes blacker at the right hand, thus showing that two-months training had greatly increased the output of the employees. If a chart like this is made with different colored pencils, the facts can be grasped more quickly than when only one color is used.
Fig. 58, at the right-hand end, shows that the workers were earning a bonus practically every day, and it also shows clearly that something was wrong during the middle part of October. The workers failed to earn a bonus at that time for the reason that the bonus work was introduced so rapidly that they did not get adequate instruction. The manager of a plant would realize such a situation at once if he had this kind of a chart before him.
At the bottom of Fig. 58 a curve is plotted to give the number of operators who earned a bonus every day. The horizontal scale for this curve is exactly the same as for the bar chart above, except that in the curve a day is represented by a line rather than by a space. In plotting curves, it is customary to represent time by lines rather than by spaces, and this curve is plotted in accordance with good practice. The scale at the left-hand edge of the lower part of the chart represents the number of workers who made the bonus. In order to plot the curve, one simply counts in the upper section of the chart the number of black blocks which are filled in for the particular day. Thus, for October 10, we see that there are seven black blocks. 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
