Steema Central

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procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
begin
  for i:=1 to 100000 do
    if i=1234 then Series1.Add(80)
    else Series1.Add(50);

  Series1.Pointer.Visible:=true;

  Chart1.Draw;
end;

procedure TForm1.Chart1AfterDraw(Sender: TObject);
var
  Min, Max: double;
begin
  Min:=Series1.YValues.MinValue;
  Max:=Series1.YValues.MaxValue;

  Chart1.Axes.Left.SetMinMax(Min-20,Max+20);
end;

function TForm1.Series1GetPointerStyle(Sender: TChartSeries;
  ValueIndex: Integer): TSeriesPointerStyle;
begin
  if ValueIndex > 0 then
    if (Series1.YValue[ValueIndex]-Series1.YValue[ValueIndex-1]>10) then
      result:=FormatPointer(Sender,ValueIndex)
    else result:=psNothing
  else
    if (Series1.YValue[ValueIndex]-Series1.YValue[ValueIndex+1]>10) then
      result:=FormatPointer(Sender,ValueIndex)
    else result:=psNothing;
end;

function TForm1.FormatPointer(Sender: TChartSeries;
  ValueIndex: Integer): TSeriesPointerStyle;
begin
  (Sender as TLineSeries).Pointer.Color:=clBlue;

  result:=psRectangle;
end;