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 In the following illustrations, curves of this kind will be noticed using the diagrammatic form rather than the actual photographs of a classified group like Fig. 141. In Fig. 141 it is regrettable that the illustration does not show a scale giving for each row the maximum and minimum height of men in that row. Some scheme, of course, was necessary to divide these men up into height classes, but the reader has no way of knowing the limits of height for each class except by referring to the title of the illustration.

Frequency charts are sometimes made for popular illustration by drawing vertical lines to represent the number of individuals found in each class designated by the horizontal scale. Thus, a representation could be made for the data of Fig. 141 by having a horizontal scale to represent heights, and drawing vertical lines to a scale by which the length of each vertical line or bar would represent the number of individuals of that particular height. The series of bars would then have the same general arrangement as the photograph of Fig. 141 representing the number of men actually seen. These bar diagrams to represent frequency are not of very great use, except possibly in advertising work where it may be necessary to get some kind of chart which can be understood by any untrained reader.

Joint board of Sanitary Control, New York City

Fig. 142. The Number of Persons Working On and Above the Sixth Floor in the Cloak and Suit Industry and the Dress and Waist Industry in New York City

This chart was made first for a wall exhibit and was later used in a widely distributed report. The co-ordinate ruling has the shape of a New York manufacturing building. By observing this illustration from the left edge of the page the reader may get the general effect of a frequency curve

In Fig. 142 an effective use has been made of the frequency-curve scheme in a report intended for wide circulation among persons who have not been trained in reading curves. The general outline of a tall New York manufacturing building is given very clearly as a field of co-ordinate ruling, on which the actual numbers of workers for any floor level can be read from the horizontal scale with a fair degree of accuracy. The numbers working below the sixth floor are very large, and only those on and above the sixth floor are shown.