An apparatus for sampling tissue includes a tissue engaging member for engaging and retaining a sample of a tissue structure, and a cutter surrounding the tissue engaging member. The apparatus includes a test fixture for housing a hydraulic component to be tested, a first fluid reservoir containing fluid substantially free of contaminants, contaminant monitoring and pressure monitoring systems for monitoring the respective contaminants at, and the pressure drop across, the inlet and the outlet of the test fixture. The medium has a wobbling groove that has a depth falling within the range of 2. Each different blur pattern can be combined with one or more of the other blur patterns non-destructively.