protected static function get_toggle_checksum($qubaid, $questionid,
            $qaid, $slot, $user = null) {
        if (is_null($user)) {
            global $USER;
            $user = $USER;
        }
        return md5($qubaid . "_" . $user->secret . "_" . $questionid . "_" . $qaid . "_" . $slot);
    }