这个怎么理解？？？有木有人知道？

function page_etime($pagestartime,$median){
	/*
	$pagestartime取页面头部的microtime();
	$median为时间位数，请使用常量
	*/
	$pageendtime = microtime();
	$starttime = explode(" ",$pagestartime);
	$endtime = explode(" ",$pageendtime);
	$totaltime = $endtime[0]-$starttime[0]+$endtime[1]-$starttime[1];
	$timecost = sprintf("%s",$totaltime);
	$time =round($timecost,$median);
	return $time;
}

示例:
echo page_etime($startime,7);