How to get previous month data from current month values

Hi Experts,

I have made one universe from BW Query in which Fiscal year period is entered in interval.

I have made a universe from that and want to develop webI reports on top of that.

In my webI reports, i have used one cross tab. In Rows section i have added Company Code and in Column section i have used Fiscal Year/Period and in Value section i have added Sales Value. I want this value of previous month.

Requirement:

Ex.

Feb'09 Mar'09 and so on...

Comp_code1 Sales of Jan'09 Sales of Feb'0f and so on....

I am getting this.

Ex.

Feb'09 Mar'09 and so on...

Comp_code1 Sales of Feb'09 Sales of Mar'09 and so on....

I hope i have clear my requirements.

Please help as soon as possible.

Thanks in Advance,

Rishit