@tlfong01 Hi! The picture representing the unstable point 2 is nice... There is only a "small" problem - there is no such point:) During the "jump", the operating point does not pass through this place (point 2 does not belong the the trajectory). So, the picture is simply wrong. Please read carefully my expalnations about the bistable mode of the negative differential resistance -
en.wikibooks.org/wiki/Circuit_Idea/….