A Manual of Design and Construction, 1938, prepared by Committee on Standards for Graphic Presentation, under procedure of American Standards Association, with The American Society of Mechanical Engineers as sponsor body.

RATE-OF-CHANGE CHARTS

A. DEFINITION. The rate-of-chonge chart ("rotio" or "semi-logarithmic" chart) is a type used for picturing the percentage or relative change in values of a series over a period of time rather than the change in absolute amounts as shown by the arithmetic chart.

1. The picture of rate of change is achieved through the use of logarithms. Rate-of-change curves can be constructed either by plotting the logarithms of the values on an arithmetic scale or by plotting the actual values on a logarithmic scale. The latter is the more usual procedure.

2. The effective use of rate-of-change charts requires an appreciation of their limitations as well as their possibilities.

B. WHEN TO USE RATE-OF-CHANGE CHARTS:

1. When the interest is in relative movement of a time series and not in the differences between amounts.

2. When it is desired to compare the relative movements of several time series.

3. When the readers are likely to be familiar with this form of chart.

4. When the usual arithmetic chart would present a misleading picture of movement.

5. For occasions when there are no minus figures included in the time series.

Note; If it is desired to present a complete picture of both rote of change end amount of chonge the dato con be presented on componion charts, one with a logarithmic amount scale and the other with the usual arithmetic scale.