public function getCheckDigits()
    {
        $checkDigits = '';
        $iban = $this->getIban();
        if (!empty($iban)) {
            $checkDigits = substr($iban, 2, 2);
        }
        return $checkDigits;
    }
public function getCheckDigits()
    {
        $checkDigits = '';
        $iban = $this->getIban();
        if (!empty($iban)) {
            $checkDigits = substr($iban, 2, 2);
        }
        return $checkDigits;
    }
public function getCheckDigits ( ) { $ checkDigits = '' ; $ iban = $ this -> getIban ( ) ; if ( ! empty ( $ iban ) ) { $ checkDigits = substr ( $ iban , 2 , 2 ) ; } return $ checkDigits ; }
return the check digits of a iban
check digits corresponding to ISO 7064

@return      string                  check digits
return the check digits of a iban check digits corresponding to ISO 7064