I did exactly that, but I want to do it in the background not front end.
As I want to also add a list box for number of days till delivery expected which would come from deliver by date-order date.
When I do what you proposed it works on the Straight Table in the front end if I make the expression (deliver by date-order date) but then when I make a list box from that calculated dimension it does not seems to relate.
This is for the warehouse to check outstanding orders, but I want them to look at it in order of importance which needs to be delivered first, thus he would choose orders with no invoice for the month we in, sort that table by number of days to deliver.
But it brings up -13 days 0 days etc as it brings in old orders we missed, so I want a list box where I choose 1 days or 2 days thus only seeing what truly needs to be supplied.