Exchange rate issuses

Hi:

We have a scenario wherein

we have foreign currency

valuation issue. We sell goods to

our customers in foreign country.

In doing export sale order is

created long before delivery is

made.In between this time there

becomes fluctuation in exchange

rate. The rate at which invoice is

booked and payment is received

varies . We at first stage want to

keep exchange rate fixed from SD.

Expert opinion is required .