how to reset the record no in the crystal report when the group header change

I have a complex report here and i need to reset my record number after the group header change
like..

Formula Code :
WhilePrintingRecords;
NumberVar counter;
if PreviousIsNull ({ado.iBarcode})  then
    counter := 1
else if previous({ado.iBarcode}) <> {ado.iBarcode} then
    counter := 1
else
counter := counter + 1