Rheology is the study of flow behavior and the subsequent deformation of materials as a result of flow. Viscosity and elastic modulus of materials are measured in rheology. The science of rheology and the characterization of viscoelastic behavior are widely used for producing many industrial products including detergents, shampoos, toothpastes, cosmetics, paints, and foods. The measurement of the flow curve is important for the first step of rheological measurements. In flow curves, the shear stress of a sample is plotted against the shear rate. Newtonian fluids are characterized by a single viscosity where the shear stress is proportional to the shear rate. Only a few of materials show this behavior. Most materials behave as non-Newtonian fluids, in which viscosity changes with the shear rate. In some cases, the rheological parameters measured with a rheometer or a viscometer do not match with the actual phenomena. This is mainly because measurement conditions are inappropriate for evaluating the actual phenomena. In rheology, it is necessary to appropriately select measurement method, conditions, and apparatuses.