PHP profiling with microtime(): Negative time?
If you want to do operations on what is returned by microtime, you have to set the "get as float" parameter to true (it defaults to false).
http://www.php.net/manual/en/function.microtime.php
$now = microtime(true);for (...) { // do something echo microtime(true) - $now; $now = microtime(true);}