You'll have to create Report Variable for the sum and use it in both places.

>In the detail band of the repoprt designer I display records, each having a field namend 'nAccepted'
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>In the summary band I display the Total of the 'nAccepted' field by selecting SUM in the "Calculations" option of the "Properties" window of the expression.
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>I need to use the value of the SUM (in the Summary band) in another expression in the Summary band of the report. The other expression is: nPercentage = (nAnotherValue / the sum of nAccepted==>*SUMmed from the Detail band).
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>Is this possible?
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>Thanks in advance!