Page:Graphic methods for presenting facts (1914).djvu/170

 from the engineering department, the factory was able to ship practically no cars during the month of January, though the schedule shows that one hundred and fifty cars should have been made that month. During February, the factory produced cars but fell further behind schedule constantly, as can be seen by the difference between the angle of the schedule line for February and the angle of the actual output line for February.

Fig. 134. Production Schedule and Actual Output of an Automobile Factory for One Year

The schedule is shown by the straight lines drawn according to the desired output per week. Actual output is indicated by the waving line showing at any date the total number of autos shipped since the beginning of the year. Note the co-ordinate paper of letter-sheet size and the scheme for marking off weeks and months so that any fiscal year may be shown on this standard ruled paper

It must be remembered that with cumulative curves the angle between the curve and the horizontal line gives the rate of production per unit of time. The angle of the curve on the page gives much valuable information to the reader. It is for this reason that cumulative curves are sometimes much more useful than curves in which the rate of output is plotted horizontally from time to time. In the cumulative curve the total output is plotted, and changes in the rate