Page:Graphic methods for presenting facts (1914).djvu/283

 one-half in the normal size of the payroll. The plant was shut down at the end of the fiscal year in order that an inventory might be taken.

The notes at the left-hand side of the card are absolutely essential to explain unusual conditions affecting the curves. In two years after an event, most managers are entirely unable to explain certain peaks or valleys in a curve, though these extreme fluctuations may be due to such events as fires, floods, or strikes. Unless the causes of unusual fluctuations are recorded, the curves would have far less than their possible utility to any new man who must take up the manager's task as his assistant or as his successor. An example of the kind of information which should be noted on the curve-card margin came up in a large public-service company, where the manager was for several minutes unable to explain a very great fluctuation which had affected the earnings of a trolley company some two years before. After careful study to explain the drop in the curve, he finally recalled that this trolley line was in a city where all cars must pass over a drawbridge between two sections of the town. At the time in question a steamer had collided with the drawbridge, making it impossible for about two weeks for any street car to cross. This accident caused the earnings of the trolley line to drop greatly during the whole of the two-weeks period. The cause of the unusual condition for the curve should have been recorded for future reference.

In Fig. 207 we have the curves for three succeeding years placed one above the other, so the eye can glance up and down the vertical lines for months and see instantly the changes which have occurred during the entire period. As automobile sales are very greatly affected by the weather conditions of different seasons of the year, these curves are important. Though weather conditions have affected the curves quite largely, we can see, by comparing the curves for 1910 and 1911, that probably conditions of management as well as weather conditions caused smaller shipments in November and December, 1911, than in those same months of 1910, when shipments were quite good. The card for 1912 is shown with the curve incomplete, just as the manager might have seen it early in the month of February, 1912, after the January reports had been received, tabulated and plotted. As Fig. 207 shows curves which are true records of the real happenings in an automobile plant, they are worthy of study for practice in curve interpretation. Notice that the changes from July to August, in 1911 and 1912, are readily seen because each curve card begins by repeating the record