instruments.go
func (d *Derive) Update(v float64) {
	p := atomic.SwapUint64(&d.value, math.Float64bits(v))
	d.rate.Update(v - math.Float64frombits(p))
}
func (d *Derive) Update(v float64) {
	p := atomic.SwapUint64(&d.value, math.Float64bits(v))
	d.rate.Update(v - math.Float64frombits(p))
}
func ( d * Derive ) Update ( v float64 ) { p := atomic . SwapUint64 ( & d . value , math . Float64bits ( v ) ) d . rate . Update ( v - math . Float64frombits ( p ) ) }
// Update update rate value based on the stored previous value.
Update update rate value based on the stored previous value .