Crystal Reports Rolling 12 Month Chart

I have been tasked with creating a report of closed service tickets for a given month.  This report would also need to have a chart with closed ticket totals from the previous 12 months.

I've read multiple forums and tried to figure it out myself without any luck.

My report is setup as follows:

CallLog.CallType - Total of all sub call types

          CallLog.Extcaltyp - Lists each sub call type and the number of closed tickets for that category for the month

I have the grand total of all closed tickets at the bottom of the report

In the Select Expert, I use CallLog.ClosedDate to determine the month I would need to report on.

I am also using CallLog.GroupName to narrow down the groups who closed the tickets.

Where I am stumped is specifying the previous 12 months closed tickets in the chart.  I've inserted a chart but can't seem to figure out where to specify the previous 12 months.

I appreciate any help anyone can provide.

Thanks,

Tom