A rotational viscometer is a device used to measure the viscosity of fluids. It works by rotating a spindle or cylinder in the fluid and measuring the resistance to this motion. The viscosity is determined based on the torque required to maintain a constant speed of rotation, providing valuable information about the fluid's flow characteristics. These instruments are commonly used in various industries, including food, pharmaceuticals, and cosmetics, to ensure product quality and consistency. By understanding viscosity, manufacturers can optimize formulations and processes, leading to better performance and stability of their products.