The entries you make in the Exchange Rate window will affect only the transaction that you are currently entering. If you want to change the exchange rate for all future transactions that use this currency, select the
Update Current Exchange Rate in the Currency List with Transaction Exchange Rate option.
Select this option if you want the rate you enter in the Transaction Exchange Rate field to be used for future transactions in this currency. The transaction exchange rate will then become the current exchange rate for all future transactions in this currency.