Abstract: A reader of a code represented by a coded array mounted on a surface and sisting of a material differing in its electrical conductivity from its surroundings comprises a pair of electrodes supported in a body movable across the surface. The pair of electrodes can be capacitively coupled, without contact, with spaced coupling sites forming part of the array. The electrodes carried by the reader body form the free ends of an open electrical circuit which has a voltage source and a detector in series. The voltage source is a signal generator applying a steady-state AC to the electrodes. The reader is movable relative and parallel to the coded surface with at least one of its electrodes above the coupling sites, the AC frequency being so selected in relation to the rate of motion that for each capacitive coupling, the measurement takes place in steady-state.