Exchange rate in MIGO.

Hi,

Could some one please tell me , what exchange rate is considered while doing MIGO. I have a PO which is 2 months old, with exchange rate of say 45.65. While doing MIGO /Service entry sheet, New exchange rate is being considered say 48.45. My requirement is that , when I am doing MIGO/Service entry sheet for a PO of 2 months old, OLD rate should be applicable and not the new one.

Where is the setting for the same and I have not checked the fixed exchange rate in PO as this impacts MIRO and not MIGO.

Regards,