A rotational viscometer is an instrument 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 specific rotational speed, providing valuable data about the fluid's flow characteristics. These devices are commonly used in various industries, including food, pharmaceuticals, and cosmetics, to ensure product quality and consistency. By understanding a fluid's viscosity, manufacturers can optimize formulations and processes, leading to better performance and stability of their products.