I can scale my application smaller, but now i want to go to a bigger scale and then back my normal scale

I have am trying scaling my application, make it smaller, normal size, bigger and back to normal size again
well thats what im trying to achieve but my code isnt working properly.

It can go smaller, but it cant go bigger or back to the original size. Could someone look at it?

var
CurrentScreenWidth := Screen.Width;
CurrentScreenHeight := Screen.Height;
OriginalScreenWidth := Screen.Width;
OriginalScreenHeight := Screen.Height;


Procedure TForm1.Smaller1Click(Sender: TObject);
begin
CurrentScreenWidth := CurrentScreenWidth + 100;
CurrentScreenHeight := CurrentScreenHeight + 100;
Form1.ScaleForm(Form1,CurrentScreenWidth,CurrentScreenHeight);
end;

procedure TForm1.ScaleForm(F: TForm; ScreenWidth, ScreenHeight: Integer);
begin
   F.Scaled := True;
   F.AutoScroll := False;
   F.Position := poScreenCenter;
   F.Font.Name := 'Arial';
   if (Screen.Width <> ScreenWidth) then begin
     F.Height :=
         LongInt(F.Height) * LongInt(Screen.Height)
         div ScreenHeight;
     F.Width :=
         LongInt(F.Width) * LongInt(Screen.Width)
         div ScreenWidth;
     F.ScaleBy(Screen.Width,ScreenWidth) ;
   end;

   if (Screen.Width = ScreenWidth) then begin
     F.Height :=
         LongInt(F.Height) * LongInt(Screen.Height)
         div ScreenHeight;
     F.Width :=
         LongInt(F.Width) * LongInt(Screen.Width)
         div ScreenWidth;
     F.ScaleBy(Screen.Width,ScreenWidth) ;
   end;
end;

Procedure TForm1.Bigger1Click(Sender: TObject);
begin
CurrentScreenWidth := CurrentScreenWidth - 100;
CurrentScreenHeight := CurrentScreenHeight - 100;
Form1.ScaleForm(Form1,CurrentScreenWidth,CurrentScreenHeight);
end;

How do I go smaller and bigger and back to the original size again.
If i go smaller that works, but if i go bigger it keep going smaller.

Weird?

Ben