code: public final void sample()
    {
      synchronized (_lock) {
        long count = _totalCount.get();
        long lastCount = _lastAvgTotalCount;
        _lastAvgTotalCount = count;
  
        long sum = _sum.get();
        double lastSum = _lastAvgSum;
        _lastAvgSum = sum;
  
        if (count == lastCount) {
          _avg =  0;
        }
        else {
          _avg = _scale * (sum - lastSum) / (double) (count - lastCount);
        }
      }
    }
docs: Return the probe's next average.