Results from oscillation tests performed with rotational rheometer can be corrupted due to huge instrument inertia contributions, related to the periodic acceleration and deceleration of the motor shaft. In a rheometer the torque output of the motor is composed of the torque required to overcome the instrument inertia and the torque deforming the sample. The torque contributions for inertia increase with the applied frequency to the power two and usually dominate the instrument response for low viscosity test samples. Rotational rheometers with a separate transducer are much less susceptible to inertia effects, since the sample torque is determined independently from the motor torque.