code: func NewDeriveScale(v float64, d time.Duration) *Derive {
  	return &Derive{
  		value: math.Float64bits(v),
  		rate: Rate{
  			time: time.Now().UnixNano(),
  			unit: d.Seconds(),
  		},
  	}
  }
docs: // NewDeriveScale creates a new derive instruments with the given unit.