Create a on/off or toggle butto

That KB article is a little misleading. You don't need a variable to do a toggle button just create a button or shape with a selected state and no visited state, this will toggle. To create an event that toggles add to triggers to that button one to do something when the state is equal to selected and one to do something when it is not selected, much easier and doesn't need you to monitor the state of the variable when the slide is revisited.