private void changeNanosecond(){
    if (fIsPlus){
      fNanosecond = fNanosecond + fNanosecondIncr;      
    }
    else {
      fNanosecond = fNanosecond - fNanosecondIncr;      
    }
    if(fNanosecond > MAX_NANOS){
      stepSecond();
      fNanosecond = fNanosecond - MAX_NANOS - 1;
    }
    else if (fNanosecond < MIN_NANOS){
      stepSecond();
      fNanosecond =  MAX_NANOS + fNanosecond + 1;
    }
  }