if (stdDev < 0) { System.err.println("Warning: stdDev value = " + stdDev + " -- rounded to zero."); stdDev = 0; }
  public void calculateDerived() {    mean = Double.NaN;    stdDev = Double.NaN;    if (count > 0) {      mean = sum / count;      if (count > 1) {	stdDev = sumSq - (sum * sum) / count;	stdDev /= (count - 1);	stdDev = Math.sqrt(stdDev);      }    }  }