To display percentages or total count, use a tool tip. Hold your cursor over a horizontal bar or pie section.
Percentages are calculated as follows:

For counted elements, the percentage is the number of elements experiencing events for a given value of the criterion, divided by the total number of elements in the summary.
For example, for elements counted by the criterion severity, 12 (14 percent) for the value Critical indicates that 12 elements have critical events. This represents 14 percent of 83 elements in a summary.

For counted notifications, the percentage is the number of events for a given value of the criterion, divided by the total number of events in the summary.

For counted impact, the percentage is the sum of the impacts for all events for a given value of the criterion, divided by the sum of the impacts for all events in the summary.