Assessment of deformations that occur during heat treatment at high temperatures of materials subjected to bending stress. Monitoring is carried out by a lens system with a resolution of 0.2 µm on specimens measuring 85 x 5 x 5 mm3. The analyses can be conducted to obtain high-precision results in hot flexural strength tests, evaluations of pyroplastic deformation with the corresponding pyroplasticity index (PI) calculations, hydro-deformation tests (curvatures caused by applying water to the surface of unfired ceramic tiles), and analyses of coupling stress between layers with different thermal expansion coefficients.