Figure 128. Step curve chart
c. Pie Charts. The best comparisons to make with this type of
chart is the parts to the whole or the parts of the whole to each other.
When preparing a pie chart, you must exercise extreme care not to make
the chart so complicated that the reader cannot interpret it at a short
(1) Use of pie charts. The human eye has difficulty making two
and threedimensional comparisons. Because of this difficulty, you
should not make a comparison of sizes using circles. Bar charts make
this type of comparison best.
(a) Perception of pie chart (figure 129, part A). Figure 129
shows the difficulty the human eye has in making a comparison using
circles by comparing circles. In part A of figure 129, the circle
,000 has a diameter twice the size of the diameter in the
0 circle. However, to the human eye, the
,000 circle appears much
larger than twice the size of the 0 circle. Here the human eye is
correct because the area of the circle representing
,000 is four times
the area of the 0 circle.