&gt; <i>In Cleveland’s paradigm, the perceptual task associated with a bar chart is judging position on a scale, and the task associated with a pie chart is judging angle. They found that the length judgments for the bar chart were “1.96 times as accurate as angle judgments” for a pie chart.</i><p>In pie charts, I find it much easier to estimate a percentage than estimate the angle, perhaps just based on value range alone; 100 vs. 360.<p>I also find estimating percentage to be harder with a bar chart since there is no reference to the entire pool of data; the encompassing circle in a pie chart.