MDX Help request for 'LastPeriods; function

Hi All, Hi Bill,

I desparetly need some help with the LastPeriods function and will be gratefull for help. The scenario is follows:

For any point in Time, I want to get the average for the last 3 periods of one of my measures (NetSales). Meaning if my selected time period is say Dec, then I want the average NetSales of Sep, Oct. and Dec. However after going through BOL, I have learned that the LastPeriods function will give me what I want BUT for Oct., Nov., and Dec :(

Can someone kindly help me.

Many TIA.