Throughout the past, a number of important facts about the quantum sine-Gordon model were discovered. Among them are truly elegant Fendley-Saleur-Zamolodchikov (FSZ) relations between the Painleve III transcendent and the sine-Gordon zero-point energy at special value of the coupling constant, where the theory exhibits N=2 supersymmetry. \par In the talk I will discuss a generalization of this result to arbitrary values of the coupling. The main player in the derivation of generalized FSZ relations is the Yang-Yang functional.