code: func sumSquares(s metrics.Sample) float64 {
  	count := float64(s.Count())
  	sumSquared := math.Pow(count*s.Mean(), 2)
  	sumSquares := math.Pow(count*s.StdDev(), 2) + sumSquared/count
  	if math.IsNaN(sumSquares) {
  		return 0.0
  	}
  	return sumSquares
  }
docs: // calculate sum of squares from data provided by metrics.Histogram
  // see http://en.wikipedia.org/wiki/Standard_deviation#Rapid_calculation_methods