0CALMONTH into a variable

Hi All,

I have a Bex Query, where I have master Data object [0CALMONTH] set as filter bringing in last 18 months data from current month. Now I want to show in webi each month as a separate column in cross tab report. Since each month is reflecting shipped Tons based on Month and lag Month.

How can create a variable in webi using the object [0CALMONTH], something like [0CALMONTH]-1 for previous month, [0CALMONTH]-2 for two months ago etc..

Need help,

thanks.