// window and to the right edge of the window.
	left := c.bands[bandIdx].integrator
	right := left
	time, endTime := c.bandTime(bandIdx)
	if utilEnd := util[len(util)-1].Time - int64(window); utilEnd < endTime {
		endTime = utilEnd
	}
	acc.resetTime()
	for {
		// Advance edges to time and time+window.
		mu := (right.advance(time+int64(window)) - left.advance(time)).mean(window)