Abstract: A microparticle which is invisible to the naked eye and is marked with digitally coded machine readable information, the machine readable information being etched through the microparticle.

Abstract: An improvement to a Viterbi-type decoder for decoding convolutional error-correcting codes whereby decisions regarding which predecessor state to a given state most probably corresponds to the best path terminating in that given state are stored in association with that given state and not in association with the best path. Paths are reconstructed by searching through such stored decisions. Such searches are used to recover a number, possibly greater than one of data symbols for later output from the decoder. The larger this number, the less frequently a search need be carried out.

Abstract: Apparatus is disclosed for generating a signal representative of a co-ordinate position of a movable indicating member, the member being constructed for interacting magnetically with sensing coils. The apparatus includes a plurality of sensing coils (2 to 11) for interacting magnetically with such a member, the coils being positioned substantially in or adjacent to a real or imaginary surface in or adjacent to which such an indicating member may be moved, the sensing coils being positioned to divide an area of interest in the surface into regions, each of the coils encircling part of the area of interest and having conductors in the area substantially along region boundaries only, each of the regions being within an arrangement of the sensing coils particular to that region. A further coil (1) is positioned substantially in or adjacent to the real or imaginary surface and surrounds the entire area of interest.

Abstract: Apparatus and methods are described for finding the coefficients of minimum polynominals in a Galois field GF(2.sup.m). Such coefficients are useful in selecting tap connections for a shift register, the taps usually being connected to an EX-OR gate in a feedback connection to the input shift register stage. Where 2.sup.m -1 is prime, with the selected tap connections the shift register generates a maximal length sequence which can be used for encyphering or decyphering. Several forms of apparatus for such processes are also described.

Abstract: A graphical input tablet is described which is made up of layers of flexible material. The edges of planar conductors on the surfaces of the layers divide the layers into zones, with each layer having a unique combination of zones. When a point is indicated on the writing area of the tablet by applying pressure thereto, conductors on facing surfaces of the adjacent layers make contact and the contacts made are indicative of the position of the point.