The zero of the vertical scale should be shown on the chart. Advantages of plotting curves for different years one above the other for comparison. Contrast in shape of curves plotted in separate fields. Advantage from shading the space under a curve. Numerous dissimilar but related curves on the same sheet. Errors resulting if curves not having the same zero line are compared. A total curve plotted from several other curves. Inverse relations, one curve trending downward when another trends upward. Study of correlation by plotting a curve from the data of two other curves. The angle of a curve on ordinary rectangular co-ordinates tells nothing about the percentage rate of growth. Disadvantages of the arithmetical scale ruling for curve plotting. Advantages obtained by plotting curves on logarithmically ruled paper.

Chapter VIII. Component Parts Shown by Curves 138

Use of vertical bars with components totalling 100 per cent. Shaded area under a curve when the height of the total field represents 100 per cent. The use of several areas in a curve field which totals 100 per cent, in height. A contrasting method of showing all curves plotted separately but from the same zero line. Universal co-ordinate paper for convenience in curve plotting. Total curves with component areas so that any point on a curve totals 100 per cent for the height of the areas beneath.

Chapter IX. Cumulative or Mass Curves 149

Factory production schedules and actual outputs plotted on a cumulative basis. Curves for income and expense on a cumulative basis. Various uses for cumulative curves. Cumulative curves with lines drawn to show rate