Although in many instances the spacing of the ruHngs clearly indicates to an experienced reader that the chart is plotted on ratio ruling, it is frequently desirable to indicate the ratio basis as shown in 345 and 346. This is especially necessary if the chart covers a comparatively short range of scale since the reader might not notice the difference in spacing of horizontal lines on the grid.

Synonyms for ratio chart are logarithmic chart, semi-logarithmic chart, rate-of-change chart.

The term "ratio chart" is short and expressive. There is need for a corresponding term equally expressive to designate charts planned on the usual arithmetic basis.

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A. Arithmetic Scale and Ratio Scale.

1. On the arithmetic scale, equal vertical

distances represent equal numerical differences; that is, the distance from 1 to 2 is the same as the distance from 2 to 3 and from 3 to 4.

2. On the ratio scale, equal vertical distances represent equal percentage differences; that is, the distance from 1 to 2 is the same as the distance from 2 to 4 and from 4 to 8.

B. Key for Assistance in Selecting the Proper Scale for Three - Deck Ratio Paper.

1. If the figures of the data to be plotted

on 3-deck ratio paper fall within the range of any one of these six brackets, the four figures within that bracket indicate the scale to be placed at the 4 points of the 3-deck paper.

2. A similar key could be made for 4-