in Fig. 152 considering the curve "A", 60 per cent of all the telephone calls of this class were answered in "less than" four seconds and 76 per cent of the calls were answered in "less than" five seconds. Of course, all those calls which were observed as having been answered in "less than" four seconds are also answered in "less than" five seconds, so that the curve is on a strictly cumulative basis. In Curve "C" it can be seen that only 30 per cent of the calls of that class were answered in less than four seconds, as against 60 per cent for curve "A". Though curve "A" is higher up on the chart than curve "C", it really represents a smaller length of time required to answer telephone calls than shown by curve "C". Since twice as large a percentage of the calls were answered in "less than" four seconds, the average time for answering calls in curve "A" is certainly smaller than the average time for curve "C", yet curve "A" appears on the upper part of the chart. It is confusing to the average reader to have curves appear on the upper part of a chart when they really represent numerically smaller quantities than other curves appearing on the lower portion of a chart. Yet this is the result when curves are plotted on a "less than" basis. In order to avoid danger of misinterpretation, it seems desirable that cumulative frequency curves should be plotted on a "more than" basis. Most of the cumulative frequency curves in this book are plotted on a "more than" basis, so that curves involving the larger quantities or percentages may appear on the chart above those cumulative frequency curves for smaller quantities or percentages.
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Fig. 151. Weight of Rails per Yard in the Main Line Track of the Seaboard Air Line Railway as Published in the Annual Report to Stockholders for the Fiscal Year Ending June 30, 1912
When using the left-hand scale the chart is read on a "more
than" basis as if the words "more than" had been used
with the horizontal scale as seen in Fig. 158. If the right-hand
scale is selected the words "less than" are used
Fig. 152 and Fig. 153 show the application of the cumulative frequency curve to commercial problems. The full explanation of these
