This calculator is automatically called from the Transaction screen when a Foreign Currency paytype is used.
In the example below, the customer has chosen to pay $214US in Euro. The exchange rate (buy) is 1.155 Euro to $1US.
The system automatically calculates the number of Euro due as 247.632. At this point, the customer pays 250 Euro and change is due. Change can be given in either the base currency ($) or in Foreign Currency.
After the Convert Currency screen is closed, the system returns to the transaction screens and enters the value of the BASE CURRENCY into the payment amount field.
Since the amount received is greater than the amount due, change (or store credit) is given to the customer.