In this kind of situation, I don't really know what to expect. This is obviously a truncation/rounding problem. Having less or more than 100% is the same problem in my opinion.

To take a more classic example:

pie title Pets adopted by volunteers
    "Dogs" : 10
    "Cats" : 10
    "Rats" : 10

Every section is one third, which would give 33% for each section. To solve that (and get a total of 100%, not 99%), the only solution I can see would be to round up a section to 34%, which does not really make sense to me.

That is because of rounding.
To eliminate the problem this rounding error must be added to the biggest element in the set.
The only problem is a set of equal elements. In that case, probably you would get one element that is bigger than others

What do you think must be the behavior in the case with one third?
Sum is not 100% but 33% is very likely the most desirable in that case

pie
    "Dogs" : 10
    "Cats" : 10
    "Rats" : 10

Maybe yes ,this is more representative of the equality between each elements

Maybe yes ,this is more representative of the equality between each elements

Hi @NXML, in that case, if you're happy to have 33% / 33% / 33% not adding up perfectly to 100%, would you also be comfortable if we leave 33% / 33% / 35% adding up to nearly (but not exactly) 100%?

Another possibility would be to display the raw values, not the (rounded) percentages, on the pie chart.

But if we make this change, it would almost certainly make some folks unhappy. So we'd probably need to leave the labels as percentages by default, and have the raw values as a configurable option ... so we would still have the rounding issue with percentages anyway. So this wouldn't fix the problem. :)

[edit] and this would be a feature request, not a bug fix.