This one is hard to visualize. Often when I want a total or grand total on a report I'll add a field in the report detail and set it to be running sum. Make sure that you name the field something like txtTotal. Then in the report footer, add another control named something like txtGrandTotal and set the datasource to txtTotal. This will display the final value across the detail. Next hide the control in the body and you get a nice total at the bottom.
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Neil Squires