type
  TInitSeriesProc<T: TChartSeries> = reference to procedure(ASeries: T);

function TChartSupport.AddSeries<T>(const AName: string;
  const AInit: TInitSeriesProc<T>): T;
begin
  if MainChart = nil then
    Result := nil
  else begin
    Result := FindSeriesByTitle<T>(AName);
    if Result = nil then begin
      Result := T(TChartSeriesClass(T).Create(MainChart));
      Result.Active := False;
      Result.ParentChart := MainChart;
      Result.Title := AName;
      Result.ShowInLegend := False;
      Result.XValues.Order := loNone;
      Result.YValues.Order := loNone;
      if Assigned(AInit) then
        AInit(Result);
    end;
  end;
end;

  FMarkerX := AddSeries<TChartShape>(CMarkerXTitle, procedure (ASeries: TChartShape)
    begin
      ASeries.Pen.Width := CLineWidth;
      ASeries.Style := chasVertLine;
      ASeries.BeforeDrawValues := MarkerXBeforeDrawValues;
    end
  );