/** Adds a series to the chart */
  public void addSeries(String varName, String label) {
    XYSeries s = new XYSeries(label, false);
    SeriesInfo info = new SeriesInfo(varName, label, s, null);
    series.add(info);
    dataset.addSeries(s);

    info.register(dataFilter);
  }
  /** Adds a series to the chart */
  public void addSeries(UserFunction uf, String label) {
    XYSeries s = new XYSeries(label, false);
    Function f = new Function(uf);

    SeriesInfo info = new SeriesInfo(null, label, s, f);
    series.add(info);
    dataset.addSeries(s);

    info.register(dataFilter);
  }