Soon after disc operation, a shaded strip, which could have been caused by corrosion or protein adsorption, was observed in the inlet of the slider surface. The film thickness, which is equivalent to the magnitude of the drop of the slider edge at the outlet, was measured at different time intervals through intermittently stopping the test. Results are shown in Fig. 3. Film thickness remained fairly constant over the course of the experiments with a slight decrease at ud=21.27 mm/s.