A rheometer is a laboratory device  that measures the flow and deformation properties of materials, such as  viscosity and viscoelasticity, in response to applied forces. It's a tool used  in rheology research and is often used to analyze the rheological properties of  polymer melts, solutions, suspensions, emulsions, coatings, inks, and food  materials. Rheometers work by subjecting a sample to various types of stress,  such as shear stress and deformation, and then measuring the relationship  between the applied force and the resulting parameters. These parameters can  include shear viscosity, elastic and viscous moduli, and more. To perform high  quality analysis, it's important to properly adapt the geometry of the  rheometer to the properties and conditions of the fluid being measured.