private function addLog($string)
    {
        $currentTime = round(microtime(true) * 1000);
        $this->log .= date('d-m-Y H:i:s - ') . str_pad($string, 50, " ",
                STR_PAD_RIGHT) . "\t" . ($currentTime - $this->lastLog) . 'ms since last log. ' . "\t" . ($currentTime - $this->loggingStart) . 'ms since start.' . PHP_EOL;
        $this->lastLog = round(microtime(true) * 1000);
    }