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