Обнаружение прокрутки TMemo

TSMemo = class(TMemo)

procedure WM_HScroll(var Msg: TWMHScroll); message WM_HSCROLL;
procedure WM_VScroll(var Msg: TWMVScroll); message WM_VSCROLL;
end;

...

procedure TSMemo.WM_HScroll(var Msg: TWMHScroll);
begin
  ShowMessage('HScroll');
end;

procedure TSMemo.WM_VScroll(var Msg: TWMVScroll);
begin
  ShowMessage('VScroll');
end;