public function toHuman()
	{
		$units = array(
            "week"   => 7*24*3600,
            "day"    =>   24*3600,
            "hour"   =>      3600,
            "minute" =>        60,
            "second" =>         1,
        );

        // specifically handle zero
        if ( $this->seconds == 0 ) return "0 seconds";

        $s = "";

        foreach ( $units as $name => $divisor ) {
            if ( $quot = intval($this->seconds / $divisor) ) {
                $s .= "$quot $name";
                $s .= (abs($quot) > 1 ? "s" : "") . ", ";
                $this->seconds -= $quot * $divisor;
            }
        }

        return substr($s, 0, -2);
	}