follow these steps:
1 add a drop down list for merchants. to do this click on one of your charts, go into chart properties, go to presentation tab, select merchant and tick Dropdown select.
2. no select the date 29/3/2011 so that you can see some Merchants with less than 90 in the sum(sales) expression.
3. clcik on the drop down list icon you have just created.
4. then type =Sum(sales)<90 in the search box.
5. 2 Merchants are selected
6. click on Bookmarks-> Add bookmark
be careful to tick the box "make bookmark apply on top of current selections"
You now have a bookmark which will always select merchants with sum(sales)<90.
But be aware if you recall the bookmark and there are now Merchants with sum(sales)<90 nothing will be selected.
to check what you have done reselect 29/3/2011. recall you bookmark. the press ctrl Q to see your current selections. you will see that the selection for Merchnats is sum(sales)<90.
hope this is clear.