<?php

sleep(3);
$t = microtime(true);

for ($i=0,$max=10000; $i<$max; $i++) {
if (!class_exists('Core',false)) {require($_SERVER['DOCUMENT_ROOT'].'/classes/core/Core.class.php');}
//require_once($_SERVER['DOCUMENT_ROOT'].'/classes/core/Core.class.php');
}

echo microtime(true)-$t;
?>

// (comment the "if" or "require_once" and uncomment the other, of course ;) )