I am working on record expense screen. Which is more usable way to record expense.
Expense Amount: 4944.50 (JPY)
In Base Currency: 50 (USD)
Exchange Rate: 98.89
There are all sorts of things to consider when converting currencies. Unless the person entering the expense report can refer back to for example a credit card statement, getting it right can be a pain.
So I'd say don't ask the person entering their expenses to convert to the base currency. Let them enter in the actual currency used an provide the business with some automatic way of converting these currencies consistently. Possibly using exchange rates data from an online provider, their bank, or, even their accounting software (I know first hand that for example SAP caters for these kinds of conversions with exchange rate tables that are/can be updated on a daily basis).