chtMain  : TChart;
FValAnno : TAnnotationTool;
...
TfrmMain.chtMainMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer)
var
  HasData : Boolean;
  AnnoLst : TStrings;
begin
  ... 
  if HasData then
    Self.FValAnno.Text := AnnoLst.Text
  else
    Self.FValAnno.Text := 'No data';
  //
  if (X < Self.chtMain.Width - Self.FValAnno.Width - 5) then
    Self.FValAnno.Shape.Left := X + 10
  else
    Self.FValAnno.Shape.Left := X - Self.FValAnno.Width - 15;
  //
  if (Y < Self.chtMain.Height - Self.FValAnno.Height - 5) then
    Self.FValAnno.Shape.Top := Y + 10
  else
    Self.FValAnno.Shape.Top := Y - Self.FValAnno.Height - 15;
  //
  if (FX >= Self.chtMain.BottomAxis.IStartPos) and
    (FX <= Self.chtMain.BottomAxis.IEndPos) and
    (FY >= Self.chtMain.LeftAxis.IStartPos) and
    (FY <= Self.chtMain.LeftAxis.IEndPos) then
    Self.FValAnno.Active := True
  else
    Self.FValAnno.Active := False;
  ...
end;