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   [...]
Private
    Procedure WMGetMinMaxInfo(Var msg: TWMGetMinMaxInfo); // in Form Deklaration
    message WM_GETMINMAXINFO;
Puplic
   [...]

Procedure TForm1.WMGetMinMaxInfo(Var msg: TWMGetMinMaxInfo);
Begin
  inherited;
  With msg.MinMaxInfo^.ptMaxTrackSize Do Begin
    X := GetDeviceCaps( Canvas.handle, HORZRES ) +
                      (Width - ClientWidth);
    Y := GetDeviceCaps( Canvas.handle, VERTRES ) +
                      (Height - ClientHeight);
  End;
End;

procedure TForm1.FormCreate(Sender: TObject);
var
  Rect: TRect;
begin
    Rect := BoundsRect;
    SetBounds(
      Left - ClientOrigin.X,
      Top - ClientOrigin.Y,
      GetDeviceCaps(Canvas.handle, HORZRES) +
                   (Width - ClientWidth),
      GetDeviceCaps(Canvas.handle, VERTRES) +
                   (Height - ClientHeight ));
end;					

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  //GetDeviceCaps(Canvas.handle, HORZRES);
  //Kurz:
  Screen.Width;