public static function stop($identifier)
  {
    if (isset(self::$benchmark_starttimes[$identifier]))
    {
      $elapsed_time = self::getmicrotime() - self::$benchmark_starttimes[$identifier];

      if (isset(self::$benchmark_results[$identifier])) self::$benchmark_results[$identifier] += $elapsed_time;
      else self::$benchmark_results[$identifier] = $elapsed_time;
    }
  }