open flash chart为什么不显示图表

求助：open flash chart为什么不显示图表？
我在网上下载的open flash chart，版本是：open-flash-chart-2-Lug-Wyrm-Charmer

我运行自带的例子为什么不显示图表？而是显示的这些东西呢？

原代码如下：
/**
 * PHP Integration of Open Flash Chart
 * Copyright (C) 2008 John Glazebrook
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

require_once('../lib/OFC/OFC_Chart.php');

$title = new OFC_Elements_Title( date("D M d Y") );

$bar = new OFC_Charts_Bar_Glass();
$bar->set_values( array(9,8,7,6,5,4,3,2,1) );

$chart = new OFC_Chart();
$chart->set_title( $title );
$chart->add_element( $bar );

echo $chart->toString();
?>

显示结果：

{"title":{"text":"Tue Apr 17 2012"},"elements":[{"type":"bar_glass","values":[9,8,7,6,5,4,3,2,1]}]}


请问有大虾知道吗？急，在线等。谢谢！



------解决方案--------------------
echo gmdate('H:i:s', abs(strtotime('2012-04-17 17:43:09') - strtotime('2012-04-17 18:01:02')));

00:17:53

沉下心来，认真思考