PHP 計算頁面執行時間

<?php
$t = new executeTime;

phpinfo();
class executeTime{
    private $microtime;
    public function __construct(){
        $this->microtime = microtime(true);
    }

    public function getNow(){
            $this->__dectruct();
    }

public function __destruct(){
    if (empty($_SERVER['REQUEST_TIME_FLOAT']))
        echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次執行時間：', microtime(TRUE) - $this->microtime, '秒</div>';
    else
        echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次執行時間：', microtime(TRUE) - $_SERVER['REQUEST_TIME_FLOAT'], '秒</div>';
}

}</pre>