Well in the spirit of that request, heres an additional sub which you can add to the module. You must add the additional key value pair of 'EUR' => 1 to the rates hash or you'll have problems doing any euro conversions :)

sub euroCalc
{
    my ($self,$amount, $from,$to) = @_;
    croak("Invalid start currency") unless defined($rates{uc $from});
    croak("Invalid target currency") unless defined($rates{uc $to});
    
    # What was it in Euros
    # $amount = ($amount * $rates{$to}) / $rates{$from};
    # Now convert to target currency
    # return $amount * $rates{$to};
    
    # Or in one line
    return ($amount * $rates{$to}) / $rates{$from};
}
[download]

And some test prints

use strict;
use Calc::Euro;

my $eurocalc = Calc::Euro->new('NLG');
print $eurocalc->to_national(1), "\n"; # 2.20371

print $eurocalc->euroCalc($eurocalc->euroCalc(1,'NLG','EUR'),'EUR','NL
+G'), "\n"; 
print $eurocalc->euroCalc(1,'NLG','BEF'), "\n"; 
print $eurocalc->euroCalc(1,'NLG','EUR'), "\n";
print $eurocalc->euroCalc(1,'EUR','NLG'), "\n";
[download]

So you notice that you can go from one currency to Euros and then to your target currency. Might prove handy to someone.

Have fun :)