A machine that’s used to measure the watts (horsepower) output of an engine. A chassis dyno has large rollers upon which the drive wheels are placed. The vehicle is run up to a certain speed and put under load so the amount of power that’s being delivered to the wheels can be measured (See Horsepower and Torque). A dyno can also be used to simulate actual driving conditions when troubleshooting various derivability problems. Dynos are also used to simulate driving conditions during certain types of emissions tests.