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Liquid crystals (LCs) play a fundamental and significant role in modern technology. Recently, they have also been used in active switching, adaptive optics, and next-generation displays for augmented and virtual reality. This is due to the diverse properties of their various phases and the growing physical understanding of LCs. Our goal is to examine the applicability of a new method in determining these quantities for thermotropic uniaxial nematic liquid crystals (NLCs), even though nearly all theoretical and experimental efforts are focused on a deeper understanding of the temperature-dependent free energy behavior and other quantities related to it, especially in the vicinity of the first- and second-order phase transitions of LCs. The method that is being discussed is based on Fresnel diffraction (FD) from phase objects, which has found a wide range of precise metrological applications over the past two decades. Diffractometry is a very sensitive, accurate, and immune technique that can convert any change in the order of LCs as a function of temperature into a change in the optical phase and, as a result, a recordable change in the visibility of the light diffraction pattern from phase steps. This contrasts with interferometry, which is very sensitive to environmental changes. Theoretical investigations, numerical calculations, and comparisons of the results with experimental observations in turn demonstrate very high compliance with the output of other existing methods. As we will see, this method has the potential to not only strengthen existing approaches by addressing some of their flaws and shortcomings but also to take its place next to them.