code: func (whisper *Whisper) MinPowTolerance() float64 {
  	val, exist := whisper.settings.Load(minPowToleranceIdx)
  	if !exist || val == nil {
  		return DefaultMinimumPoW
  	}
  	return val.(float64)
  }
docs: // MinPowTolerance returns the value of minimum PoW which is tolerated for a limited
  // time after PoW was changed. If sufficient time have elapsed or no change of PoW
  // have ever occurred, the return value will be the same as return value of MinPow().