private function getRatio($rate, $time)
    {
        $gcd = $this->getGCD($rate, $time);
        $requests = $rate / $gcd;
        $time = $time / $gcd;
        $suffix = 's';
        foreach ($this->units as $unit => $sec) {
            if ($time % $sec === 0) {
                $suffix = $unit;
                $time /= $sec;
                break;
            }
        }
        return $requests . '/' . $time . $suffix;
    }