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1. "Using Filters," create a filter based on a date field. The filter appears in the Filters panel.
2. In the filter's operator, select the date comparison you would like to make.
3. In the filter's text entry box, enter an expression describing the relative date.
For instance, if you want to display all the sales numbers for the month prior to the current date, you would select "is on or after" as the operator and and in the second box you would enter MONTH-1.
(this would show you all results exactly a year prior to the date the report was run)
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