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 motor end. The motor speed is precisely controlled by control unit and sealed at motor end. The motor speed is precisely controlled by control unit and can be run in both directions. The bearing contains twelve equispaced pressure tapping around circumference and four along the axis. All are connected by light flexible plastic tube to the manometer so that the pressure head of all sixteen point can be observed at a time. The bearing can be loaded by attaching weight to the arm supported beneath it.