As the card 12 inches long is necessary for weekly records, a card of the same size can be used conveniently to show five years by months instead of using five separate 4-by-6-inch cards, one for each year. In Fig. 214, the figures at the top of the card show the

CURVES FOR THE EXECUTIVE 281

milk production each month and the total milk production for each calendar year. The notes in the left-hand margin show the dates on which calves were born.

In Fig. 215, also, curves are plotted on a card for five years by months. In this case there was no hope of getting the cost per ton below 50 cents, and the scale was accordingly so chosen that it began at 50 cents instead of at zero in order that fluctuations from month to month might be more carefully observed. As the zero line was not shown on the card, the wavy line was drawn at the bottom of the ruled portion, indicating clearly to the reader that he must not interpret the curve as though the bottom were at zero.

When using an arrangement showing five years by months on one card, considerable mental effort is necessary to get a clear interpretation of the fluctuations in the curve from year to year. In Fig. 215 certain peaks in the curve appear to have somewhat similar shape. Thus the peak for 1908 looks like the peak for 1907 until closer examination shows clearly that the low point for 1908 was in July, while the low point following the peak of 1907 came not in July, 1907, but in January, 1908. The waves themselves, although of somewhat similar shape, have peaks at entirely different times, the peak for 1908 being in February and the peak for 1907 in April.