How to see log of changing PO

Hi Experts,

I have a strange issue with currency of Purchase Order. I don't know why at first PO had currency SGD ( PO was printed out with currency SGD ) but after that it had currency VND. Every body concerned sure that they did not change any thing in that PO.

Please direct me where I can check to find out the cause is . ( such as read log file ).

Thank you very much.

Best Rgds.