Thus the modified cumulative curve may be used to show the quantities of stock on hand, additions to stock being plotted upward and reductions to stock being plotted downward. Any point on the curve then shows the ciuantities on hand at that particular time. In making a curve like this it is ordinarily the practice to strike a balance of the additions and reductions for the latest period of time, and then to change the curve only by the net amount added or taken away. Such a curve gives not only a perpetual inventory in the last point plotted, but it shows the quantity on hand at different seasons of the year as a guide for future operations. A curve of this kind can be plotted for the total number of men employed in a large organization just as well as for quantities of goods in store rooms.

Fig. 134 was photographed from a sheet of co-ordinate paper specially ruled for convenience in curve plotting. The paper is eight

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and a half by eleven inches (a standard letter-sheet size), and has coordinate ruling printed in green ink with wide margins on all four edges to allow space for lettering, scales, etc. Note in Fig. 134 that the green ink of the co-ordinate lines shows much lighter in color than the black drawing ink used for the scales and the curves. Though the co-ordinate lines are distinct enough for ease in reading they are not nearly so conspicuous as they would be if a line cut had been used instead of a half-tone. In making a line cut, the green lines of the paper must, of course, be printed as black and the color value of the green lines is entirely lost. The finished line cut shows only the relative widths of lines, not relative colors.