TCURR Table Help Req??PR's Exchange Rate???

I need to find out the exchange rate for a PR w.r.t its document date,I had the Currency Key frm the EBAN table & its doc date,but how this data can be used to find out the excahnge rate for thet PR,as in TCURR table we maintain all the exchange rates till current date.??

is there any other way to find out the exchange rate for a PR,is there any table,frm whcih I can get its data?

Rgds

vipin