public function toUTC() 
    {
        $ts = time();
        if ($this->getAttribute("timeStamp")) {
            // from NIS to UTC
            $ts = (int) $this->getAttribute("timeStamp");
            return self::$nemesis + (1000 * $ts);
        }
        else {
            // has UTC
            return $this->getAttribute("utc");
        }
    }