We get to see an Exchange Rate Entry window every time we try to post a transaction entry in Multicurrency, be it a General Entry or a Transaction in Sales or Purchasing series.
This happens whenever a valid exchange rate could not be found in the Multicurrency Exchange Rate Maintenance for the selected currency Rate Type. In some cases, the Exchange rate for certain currencies doesn’t change frequently. In these cases, we can choose to avoid this Exchange Rate Entry window by inserting an exchange rate that stays unexpired as shown below. Adding to this we need to set the Exchange Table ID to search for Unlimited Unexpired Rates as well as assigning a Transaction rate Default to either “previous Date” or “Next Date”.
Now, when we enter a transaction in Multicurrency, the system automatically assigns the recently available rate to the transaction by default until and unless we insert another new rate that would then become the new default. Remember that this setup is required for each of the transaction type if there are different transaction type for Financial, Sales and Purchasing Series provided the rate is constant for all these transaction types. Adding to this, this setting makes sense for only those currencies which stays constant for most of the time.