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

glance.

(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

representing
||content||
,000 has a diameter twice the size of the diameter in the

0 circle. However, to the human eye, the
||content||
,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
||content||
,000 is four times

the area of the 0 circle.