code: func Tickmarks(min, max float64) (list []float64, precision int) {
  	if max > min {
  		spread := niceNum(max-min, false)
  		d := niceNum((spread / 4), true)
  		graphMin := math.Floor(min/d) * d
  		graphMax := math.Ceil(max/d) * d
  		precision = TickmarkPrecision(d)
  		for x := graphMin; x < graphMax+0.5*d; x += d {
  			list = append(list, x)
  		}
  	}
  	return
  }
docs: // Tickmarks returns a slice of tickmarks appropriate for a chart axis and an
  // appropriate precision for formatting purposes. The values min and max will
  // be contained within the tickmark range.