Foreign currency transactions Requisition and Purchase Order amount

Hi,

I am working on a report which compares approved requisition amount and the associated purchase order amount. ( to see the difference between between the two documents. )

The difference is coming to be very high for foreign currency transactions.

At what point and how the currency conversion happen on a requisition and purchase order.

Can i find out the exchange rate used for the conversion for requisition and purchase order with a SQL.

Any pointers on this will be appreciated.

thx,

Megan