I have a column of values that are the result of an equation. When I try to sum these values, I do not get the correct total. I have been trying to insert a sum and selecting the formula field for the column in the field explorer.  

The column is part of an aging report and it is a column of values from this formula:  If (Datediff("d",{ART_CURRENT__TRANSACTION.Accounting_Date},{?RefDate}))+1 > 60
and (Datediff("d",{ART_CURRENT__TRANSACTION.Accounting_Date},{?RefDate}))+1 < 91 then {ARA_ACTIVITY__ACTIVITY.Amount} else 0

How do I sum this column correctly?