Here a test example.
Find a screenshot in the support forums

  with Chart1 do
  begin
    View3D:=False;
    Legend.Hide;
    Gradient.Visible:=False;
    Color:=clWhite;
    Walls.Back.Gradient.Visible:=False;
    Walls.Back.Color:=clWhite;
    Axes.Left.Grid.Hide;
    Axes.Bottom.Grid.Hide;

    AddSeries(TFastLineSeries).FillSampleValues;
  end;

  with TSubChartTool(Chart1.Tools.Add(TSubChartTool)) do
  begin
    with Charts.AddChart do
    begin
      View3D:=False;
      Axes.Left.Grid.Hide;
      Axes.Bottom.Grid.Hide;
      Left:=200;
      Width:=400;
      Height:=300;

      AddSeries(TFastLineSeries).FillSampleValues;

      with TColorLineTool(Tools.Add(TColorLineTool)) do
      begin
        Axis:=Axes.Bottom;
        AnnotationValue:=True;
        Value:=10;
      end;

      with TAnnotationTool(Tools.Add(TAnnotationTool)) do
      begin
        Text:='Annotation in SubChart';
        Shape.CustomPosition:=True;
      end;
    end;
  end;

  with TColorLineTool(Chart1.Tools.Add(TColorLineTool)) do
  begin
    Axis:=Chart1.Axes.Bottom;
    AnnotationValue:=True;
    Value:=2;
  end;

  with TAnnotationTool(Chart1.Tools.Add(TAnnotationTool)) do
  begin
    Text:='Annotation';
    Shape.CustomPosition:=True;
  end;