You have the option to add the calculation to views and reports so that each time the user clicks Save, the exchange rates are used to recalculate the common currency member(s).
Go to Analyze or Report.
Select the view or report that contains the data in local currency and common currency.
Select Design View or Design Report.
Click Properties.
Add the calculation to the Calculation on Save property and click Save.
Example View Properties:
Example Report Properties:
