Normalizing the histogram

The default vertical axis of a histogram represents the count of values that map to a particular bucket. To report the histogram as a percentage of a whole, the histogram count is normalized to add up to 1, and then the bars represent the proportionate frequency.

The following image shows the two versions of the histogram. You can see that the change appears in the vertical axis and the tooltip, where frequency is reported as a number of incidents on the upper graph, and as a percentage on the lower graph.