Offset in Web Application Designer

Hi,

i try to build a Web Application in which the the Date (0CALDAY) is addicted to the actual day and then do an offset of 7/14/31 days on it. The offset should be chosen by an Tabstrip (one for 7, one for 14, one for 31), but the Query should always be the same.

But i can't find the option in WAD to set the selection state on a variable with an offset.

Is there any possibility?

I hope you could follow my problem, i'm not an english native speaker...