If I add the values for the items in the black box, I'm showing 2.884 (which I attribute to some missing decimals) which seems in line with what the tooltip is showing you. Mind explaining the issue a bit more?
I am looking to add an average into the tooltip (all the selected values added up then divided by the total number of values). This value should yield approximately 28.84% as that is the average of the all the selected values from my original screenshot.
Ah that makes sense! It looks like we probably want to change the aggregation in the tooltip. I'm thinking something like the solution here:
Also, if you post a packaged workbook, we can take a closer look and try to give a helpful answer.