(57) A flat-panel display (1) comprising a panel (3) including intersecting row and column electrodes (11, 13) and using selected unipolar isogonal waveform signals to address each set of row electrodes (11) and each set of column electrodes. This allows display of simple geometric structures - reference lines, grids, cross-wire features and reference symbols such as boxes and line markers, structures all requiring representation by two or more picture elements in some of the colums (13). The panel matrix may be of cartesian or polar format. As example, a cross-wire feature display (1) is shown and described. Two isogonal signals, a squarewave and its inverse, are generated using two shift and store bus registers (7 & 9). Signal and electrode selection is controlled in response to input co-ordinate addrass data, using a comparator (27; 29) and an exclusive-OR gate (15; 17) to control the data input (D) of each register (7; 9).
The flat panel display (1) may be used as a graticule in an optical sight or image projection system. Alternatively it may be used as an overlay to printed, back projected, and other static images and pictures. It may be used as an accessory to a cathode ray tube or to another flat-panel electronic display. Also, it may take the form of a quasi-analogue meter display with an additional hand used to denote or record some particular value or values of the variable displayed by the main hand.