The use of “thermal-windowing” methods to decouple molecular motions in polymeric materials has recently become very popular by the introduction on the thermal analysis market of the automated TSC/RMA spectrometer. The data obtained are collected into a relaxation map which shows the several relaxation modes for the internal motions occurring at T g, below T g and above T g. A relaxation map is a set of log τ (relaxation time) versus 1/ T curves obtained at different polarization temperatures. The decoupling between the relaxation modes responsible for internal motion leads to a better understanding of their coupling characteristics. At T g, the Arrhenius lines gather into packs of lines which converge to a single point, the compensation point. The coordinates of the compensation point are dependent on the actual state of the glass. The thermally stimulated current characteristics of PMMA are studied here to demonstrate the power of the analysis provided by the TSC/RMA spectrometer when thermal-windowing is used. In particular, the experimental results are replotted as the variation of the free energy of activation versus temperature for each polarization temperature, T p and the values of the free energy, enthalpy and entropy of activation are calculated at T p. Plots of the thermo-kinetic variables against T p, when T p varies, leads to characteristic results of the relaxation map: T g is characterized by a maximum in the entropy of activation (and also of the enthalpy), and by the intercept of two compensation lines, one positive and one negative, as T g is crossed resulting in a “Z structure” for the relaxation lines. It is shown how the Z structure and the Z line, which it defines, relate to the corresponding positive and negative compensation lines. Finally, a new characterization method to define T g from the Z structure is introduced.