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. The foregoing examples may serve to point out the mental effort necessary in reading horizontally if the danger of misinterpretation is to be avoided. If the curves for these same years 1907 and 1908 were plotted on 4-by-6-inch cards, and one card placed above the other as in Fig. 207, there would be no possibility of error on the part of the reader. The eye would follow the vertical lines and see at once that there was no great similarity in the two waves. Having five separate cards causes the reader to take more time in handling cards in order that he may save mental effort and avoid error in interpreting the yearly waves. Having five years on one card saves handling the cards, but it takes more mental effort to be accurate in reading the curve horizontally. The choice between five cards of one fiscal year each and one card for five years must rest with the judgment or the habit of mind of each individual person.