In a chart of this kind some estimates and approximations must be made because it is usually impossible to obtain accurate data to the extent desired. For work of this nature it will ordinarily be found that a little "horse-sense", used in making estimates for missing data, will permit the construction of a chart giving an astonishingly large number of suggestions useful in determining the policy of a business, so that expansion and contraction may be in harmony with the basic financial conditions of the country.

Chapter VII COMPARISON OF CURVES

THERE are many men who from long experience have become so skillful that they can glance down a column of figures and obtain quickly a good idea as to the high points and the low points shown by the figures taken as a whole. When it comes to considering two or three columns of figures simultaneously to see whether there is a similarity in the fluctuations shown by the various sets of figures, the number of men who can intelligently grasp the facts presented are rather few. It is in just such problems as these; where a number of different sets of data must be compared, that curves have tremendous advantage over presentation by columns of figures. A man must be almost a genius to grasp quickly the facts contained in several parallel columns of figures, yet anyone of average intelligence can interpret correctly a chart which has been properly made for the presentation of curves. Though there are numerous convenient methods which are useful in comparing curves, we can take up here only the few of those which are likely to be of most frequent use to the average reader.