code: func (h *Histogram) Mean() float64 {
  	if h.totalCount == 0 {
  		return 0
  	}
  	var total int64
  	i := h.iterator()
  	for i.next() {
  		if i.countAtIdx != 0 {
  			total += i.countAtIdx * h.medianEquivalentValue(i.valueFromIdx)
  		}
  	}
  	return float64(total) / float64(h.totalCount)
  }
docs: // Mean returns the approximate arithmetic mean of the recorded values.