procedure TForm1.Chart1AfterDraw(Sender: TObject);
var
  i : Integer;
  Valx,ValY : Integer;
begin
  for i := 0 to series1.Count - 1 do
    begin
      ValX := Series1.CalcXPosValue(Series1.XValue[I]);
      ValY := Series1.CalcYPosValue(Series1.YValue[I]);
      Series1.ParentChart.Canvas.Pen.Style := psSolid;
      Series1.ParentChart.Canvas.Pen.Color := ClRed;
      Series1.ParentChart.Canvas.Brush.Style := bsClear;
      Series1.ParentChart.Canvas.Sphere(Valx,ValY,0,5);
    end;
end;