The dotted line shows the erroneous impression which would be obtained by the reader if he should interpret Fig. 72 by the diameters instead of by the areas of the circles

diameter basis rather than on the area basis to which the circles were drawn, one gets an interpretation like that indicated by the dotted line in Fig. 73. By comparing the dotted line with the solid curve the reader may see the extent of the error which arises if circles are compared on a diameter basis after being drawn on an area basis.

Fig. 74 gives a good idea of the utility of the curve method for showing concisely a large quantity of data. If the figures for the price of cement had been expressed in dollars and shown in a long numerical column, there would be very few readers who would take the

CURVE PLOTTING

trouble to follow the table of figures and notice tbe fluctuations from year to year. The curve, however, gives all the variations in price at a glance and shows in most striking manner the great reduction which occurred in the price of cement as manufacturing facilities improved and increased. A curve of this kind greatly stimulates thought, for one immediately wishes to know the cause of each of the peaks and of each of the valleys in the curve. One gets a vista of recurring periods of financial boom and of financial depression, and a glimpse of such factors as new developments in methods of manufacturing cement and the constantly increasing demand for the product.