This assumes your data looks like this
Group Month Sum
A Jan 12
A Feb 23
etc. The percent is a calculated field (table calc set to give the % by month for all groups)
Edit: Aaaand I'm pretty sure I just created that in v8 - do you have the beta?
table.twbx.zip 14.5 KB
Thanks, Alex. This shows what the Measure Names and Measure Values pills are for, which I didn't know until now. Really appreciate it. Great job!