Choosing and reading graphs
A circle graph divides 360° in proportion to the parts; a line graph is the one that shows a trend over time.
A worked example
A category holding 20% of a circle graph takes up 0.20 x 360 = 72° of the circle.
The mistake people actually make
A vertical axis that does not start at zero makes small differences look dramatic. Histogram bars touch because the data is continuous; bar graph bars do not.