-Returns the exchangerate in database format for the invoice according to that invoice's transdate.
-Returns 'sell' for sales, 'buy' for purchases.
+Returns 1 immediately if the record uses the default currency.
+
+Returns the exchangerate in database format for the invoice according to that
+invoice's transdate, returning 'buy' for sales, 'sell' for purchases.
+
+If no exchangerate can be found for that day undef is returned.
+
+=item C<forex>
+
+Returns 1 if record uses a different currency, 0 if the default currency is used.