A chassis dynamometer is a device used to measure the power output and performance of a vehicle's engine while it is in motion. It consists of rollers that simulate road conditions, allowing the vehicle to be tested as if it were driving on the street. This equipment helps in assessing various parameters like horsepower, torque, and emissions. Chassis dynamometers are commonly used in automotive testing facilities, research and development, and by performance tuning shops. They provide valuable data for engineers and mechanics to optimize vehicle performance and ensure compliance with emission standards.