@AI1 it looks like the employee record uses the base currency of the employee subsidiary.
The challenge for me is how I'm going to pick up the exchange rate automatically.
I was thinking maybe I'll just create a custom field and use a single currency approval limit field (e.g., root parent base currency which is USD). That way, it's uniform and no conversion is needed.
The transaction then would always be converted to USD. But I'm not sure how to get the current exchange rate from the exchange rate history page.
For example, if the transaction currency is EUR but the subsidiary currency is GBP, I would have to make a conversion from EUR to USD (to be the same as the approval limits).