code: protected function getNewRatio($key, $limit, $milliseconds)
      {
          $lastRequest = $this->getLastRequest($key) ?: 0;
          $lastRatio   = $this->getLastRatio($key) ?: 0;
  
          $diff = (microtime(1) - $lastRequest) * 1000;
  
          $newRatio = $lastRatio - $diff;
          $newRatio = $newRatio < 0 ? 0 : $newRatio;
          $newRatio+= $milliseconds/$limit;
  
          return $newRatio;
      }
docs: Get new ratio
  
  Assuming we're making a request, get the ratio of requests made to
  requests allowed
  
  @param string $key  - A unique key for what we're throttling
  @param int $limit   - How many are allowed
  @param int $milliseconds - In this many milliseconds
  @return float