The apparatus consists of a plain steel shaft encased in a bearing and directly driven by a small electric motor. The bearing is freely supported on the shaft and sealed at the motor end. The motor speed is precisely controlled by a control unit and sealed at the motor end. The motor speed is precisely controlled by a control unit and can be run in both directions. The bearing contains twelve equi-spaced pressures tapping around the circumference and four along the axis. All are connected by a light flexible plastic tube to the manometer so that the pressure head of all sixteen points can be observed at a time. The bearing can be loaded by attaching weight to the arm supported beneath it.