Page:Graphic methods for presenting facts (1914).djvu/382

 6. If numerical data cannot be included in the chart, it is well to show the numerical data in tabular form accompanying the chart.

7. All lettering and all figures on a chart should be placed so as to be read from the base or from the right-hand edge of the chart.

8. A column of figures relating to dates should be arranged with the earliest date at the top.

9. Separate columns of figures, with each column relating to a different date, should be arranged to show the column for the earliest date at the left.

10. When charts are colored, the color green should be used to indicate features which are desirable or which are commended, and red for features which are undesirable or criticized adversely.

11. For most charts, and for all curves, the independent variable should be shown in the horizontal direction.

12. As a general rule, the horizontal scale for curves should read from left to right and the vertical scale from bottom to top.

13. For curves drawn on arithmetically ruled paper, the vertical scale, whenever possible, should be so selected that the zero line will show on the chart.

14. The zero line of the vertical scale for a curve should be a much broader line than the average co-ordinate lines.

15. If the zero line of the vertical scale cannot be shown at the bottom of a curve chart, the bottom line should be a slightly wavy line indicating that the field has been broken off and does not reach to zero.

16. When curves are drawn on logarithmically ruled paper, the bottom line and the top line of the chart should each be at some power of ten on the vertical scale.

17. When the scale of a curve chart refers to percentages, the line at 100 per cent should be a broad line of the same width as a zero line.

18. If the horizontal scale for a curve begins at zero, the vertical line at zero (usually the left-hand edge of the field) should be a broad line.

19. When the horizontal scale expresses time, the lines at the left- and right-hand edges of a curve chart should not be made heavy, since a chart cannot be made to include the beginning or the end of time.

20. When curves are to be printed, do not show any more coordinate lines than necessary for the data and to guide the eye. Lines 1/4-inch apart are sufficient to guide the eye.