The Currency Calculator window allows you to calculate either the exchange rate or a currency amount when entering multicurrency transactions. If you enter two of the following components - exchange rate, originating currency amount and local currency amount - the Currency Calculator window will calculate the third component for you. For example, if you have £100 and you know the exchange rate for United States dollars is .69, enter those amounts, and the Currency Calculator will calculate the value of your currency in United States dollars - in this case, 144.93 United States dollars.llars.