A valve apparatus for medical applications, comprises a flexible member extending across a lumen through which a flow of materials is to be controlled. The method includes: dividing each of physical programming units into a data bits area and a spare bits area; generating first data management information corresponding to first data according to a first write command and the first data; determining whether the first data is compressible; and generating first data compression information corresponding to the first data. This invention achieves total transmittance of more than 50% when light is incident on the normal direction of the incident plane at a predetermined angle \u03b1 and achieves 1. The guide wheel is moveable between a retracted position and an extended position wherein when the guide wheel is in the retracted position, the feed length is substantially equal to a distance between the outer surface of the guide wheel engaging the ground and the cutting head. The light scattering particles are spheres of titanium dioxide suspended in silicone.