Calculate percentage of positive and negative numbers for a pie chart

[splinters]

Hi guys, first post.
I am trying to complete a teacher assessment sheet and one thing I need to do is show any many students meet their target grade, how many miss it and how many exceed.
I have a column that compares the target with achieved and its a mixture of positive and negative numbers. As its to one decimal place its unlikely that many will hit 0 as a difference.
How can I get a pie chart which summarises this into two (possibly three) segments; (achieved), missed or exceeded.
I'm thinking it will involve another column or cell where these values need to be processed before the pie chart can be produced but I'm a bit stumped here. The numbers are in cells Q7:Q32.

Any help welcome and apologies if this is in the wrong section.

[jason.b75]

Take a look at this link, see if it helps. https://chandoo.org/wp/group-small-s...in-pie-charts/