public function timeClass($time, $slow = null, $fast = null)
    {
        $slow = $slow ?: 0.02;  // 20ms
        $fast = $fast ?: 1e-3;  //  1ms

        if ($time <= $fast) {
            return 'timeFast';
        }

        if ($time <= $slow) {
            return 'timeMedian';
        }

        return 'timeSlow';
    }