Don't Summarize missing from tooltips

Hi All,

I'm trying to add a text value to a tooltip on a line chart, using a lookup table for the month, so when users hover over the month they can see any external factors that might have effected the numbers for that month

E.g

Month  -   External Factor

January -  No issues

February - Train Strikes

March -      No issues

April -        Weather problems

etc

When I add the external factor to the tooltip field on a line graph, it doesn't give me the option to select don't summarize, it only has first, last, count, so the factors are not showing as they are for each month in the table.

Anyone come across this and found a way around it?

Thanks

Sarah