Current usage of Zend_Currency_CurrencyInterface::getRate() requires to return 1/$rate instead of $rate

Code:

class ExchangerService implements Zend_Currency_CurrencyInterface
{
    public function getRate($from, $to)
    {
        if ('RUB' == $from && 'USD' == $to)
            return 0.033333;
        elseif ('USD' == $from && 'RUB' == $to)
            return 30;

        return 1;
    }
}

$zc = new Zend_Currency('RUB', 'ru_RU');
$zc->setService(new ExchangerService());
$zc->setValue(100, 'USD'); // expected exchange 100 USD to 3000 RUB (rate is 30 from USD to RUB)
echo $zc->toCurrency();

Result:

3,33 руб.

Expected value:

3 000,00 руб.