On a chassis dyno, the car stands with its driven wheels on heavy steel rollers. Straps hold it in place and a large fan provides cooling. In a fixed gear the driver goes to full throttle, from low to high engine speed.
The dyno measures the force the wheels put into the rollers and calculates power and torque across the whole rev range from it. The result is a curve, not a single number: you see where the engine is strong and where it holds back.
Because conditions matter, we repeat a run until the values are stable. Only then do we compare.
