A portable combination clipboard and book holder has a flat generally rectangular board with a hinged book support at one end connected by stop hinges to allow it to be pivoted between a horizontal stored position on the top surface of the board and an upright in-use position. This may be formed by plasma etching the front side or the back side of the silicon wafer to cut a plurality of trenches or holes deep enough to extend for at least part of its thickness into a doped buried layer of opposite type of conductivity of the substrate and of the epitaxial layer grown over it. The valve units are arranged concentric to and along the longitudinal axis of each filter element. The first support defines a first raised portion. The organization and groupings may be shared with others.