Abstract: According to the disclosure, electrochromic display apparatus is provided, comprising, an electrolyte containing an electrochromic material, a plurality of display electrodes in the electrolyte, the display electrodes being connected in at least one group to enable selection of display electrodes, means for selecting at least some display electrodes, means to effect deposition of a visible coating of colored species derived from the electrochromic material onto the selected display electrodes, and means to effect deposition of an invisible coating of the colored species onto all unselected display electrodes, whereby the potentials of selected and unselected display electrodes are equalized.

Abstract: A three color gun cathode ray tube has convergence correction signals derived from digital signals stored in a digital data store. The screen of the tube is divided into a plurality of areas and a digital correction signal derived for each area. The system is arranged so that when the three beams are scanning a particular area the digital correction signal associated with that area is read out from the digital store, passed through a digital to analog converter and then applied to the convergence coils of the tube.