code: func NewSampledTimer(base tally.Timer, rate float64) (tally.Timer, error) {
  	if rate <= 0.0 || rate > 1.0 {
  		return nil, fmt.Errorf("sampling rate %f must be between 0.0 and 1.0", rate)
  	}
  	return &sampledTimer{
  		Timer: base,
  		rate:  uint64(1.0 / rate),
  	}, nil
  }
docs: // NewSampledTimer creates a new sampled timer.