Reaction torque sensor uses a sensing element that is connected between the drive member and the driven member. Under dynamic conditions the sensing element will be in motion, thereby making the torque measurement more difficult. Not only the overall bandwidth of the system decrease, but the original torque will also be changed because of the inclusion of an auxiliary sensing element. The reaction method of torque sensing eliminates these problems to a large degree. This method is used to measure torque in a rotating machine. The supporting structure of the rotating machine is cradled by releasing its fixtures and the effort necessary to keep the structure from moving is measured. It is widely used in dynamometers that determine the transmitted power in rotating machinery through torque and shaft speed measurements.