problem in take opening balance

Friends i want to take opening balance when i open a report between date parameter it show the opening balance so kindly help me out these

actually i have three columns "description" "debit" "credit" in crystal report now i want to add 1 more field which come throuhd formula which is opening balance

i have a data of debit credit from 2006

but user choose to show the data from 2008 so i want that the balcne from sum of debit and credit side between 2006 to 2007 end come in the shape of opening balance in the report and then add the debit and credit side of report into opening balance

i put a foll开发者_Go百科owing fromual bt not accept it

sum ({vr_detail.debitT})-sum({vr_detail.creditT}) > {?strtdte}

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you can pass that value from Windows Forms from the database too.