Determine execution time in PHP File

This code will determine the time taken for a php script to execute correct to 0.000000000000001 seconds.

<!-- put this at the top of the page --> 

<?php 

   $mtime = microtime(); 

   $mtime = explode(" ",$mtime); 

   $mtime = $mtime[1] + $mtime[0]; 

   $starttime = $mtime; 

?> 

<!-- put other code and html in here -->

<!-- put this code at the bottom of the page -->

<?php 

   $mtime = microtime(); 

   $mtime = explode(" ",$mtime); 

   $mtime = $mtime[1] + $mtime[0]; 

   $endtime = $mtime; 

   $totaltime = ($endtime - $starttime); 

   echo "This page was executed in  ".$totaltime."  seconds"; 

?>