dynamometer

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is the instrument used to measure force or power, such as the horsepower developed by an internal combustion engine. Horsepower can be determined by measuring the torque (turning power) produced by the rotating output shaft or by placing the driving wheels of a car on large rollers that drive a dynamometer. The latter method is often regarded as a better indicator of actual road performance. The dynamometer can be loaded to put the engine through a range of simulated operating conditions. Dynamometer testing is commonly employed to assess the performance characteristics of automotive fuels and lubricants.