type
  TNotifyEvent = procedure
                (Sender: TObject) of object;

procedure TThirdComponent.Start;
begin
  inherited; //This calls TSecondComponent.Start
  FState := stStarted;
  if Assigned(OnStart) then OnStart(Self);
  if Assigned(OnStateChange) then 
    OnStateChange(Self, State);
end;

procedure TThirdComponent.Stop;
begin
  inherited;  //This calls TSecondComponent.Stop
  FState := stStopped;
  if Assigned(OnStop) then OnStop(Self);
  if Assigned(OnStateChange) then 
    OnStateChange(Self, State);
end;

constructor TThirdComponent.Create(AOwner: TComponent);
begin
  inherited;
  //This is were you initialise properties, and create
  //and objects your component may use internally
  FState := stStopped;
end;

destructor TThirdComponent.Destroy;
begin
  //This is where you would destroy
  //any created objects  
  inherited;
end;

procedure TForm1.ThirdComponent1Start(Sender: TObject);
begin
  Caption := 'Start';
end;

procedure TForm1.ThirdComponent1Stop(Sender: TObject);
begin
  Caption := ThirdComponent1.ElapsedTime;
end;

procedure TForm1.ThirdComponent1StateChange
  (Sender: TObject; State: TState);
begin
  btnStart.Enabled :=
     ThirdComponent1.State = stStopped;
  btnStop.Enabled :=
     ThirdComponent1.State = stStarted;
end;