Abstract: An electrical assembly including a digital logic circuit, an analogue processing circuit and an analogue power circuit is connected to test equipment. Test data from the equipment is supplied to the circuits via a shift register divided into three serial portions. One portion is connected between the digital circuit and the processing circuit, another portion is connected between the processing circuit and the power circuit, the final portion being connected at the output of the power circuit. The portions can isolate the circuits from each other and supply test data to the circuit under test. The test data output from the circuit is clocked along the register to its output.

Abstract: In a cathode-ray tube display system, signals defining the coordinates of the element of the screen on which the cathode-ray beam is incident in its raster scan are supplied to a comparator together with signals defining the coordinates of a series of points defining the image to be displayed. The comparator derives a brightness-weighting signal in respect of each element in accordance with the proximity of that element to those of the points defining the image within a predetermined proximity. The predetermined proximity may be equal to the separation between the points. The system also includes a store, brightness-weighting signals being added together in the store to produce a total signal for each element that is used to control bright-up of the element.

Abstract: A head-up display involving display of pitch-bar symbols in the line of sight of an aircraft pilot is generated using raster scanning of a cathode-ray-tube screen and bright-up in accordance with stored information relating to the wings-level or other datum attitude of the aircraft. Variation of the pitch-bar mapping in the display area to follow change of attitude of the aircraft is made through transformation in accordance with pitch and bank angles applied to the point-by-point progression of the raster scan, and the visual staircase effect of symbols inclined to the line-scan is reduced by controlled variation in brightness from point to point. Each point (x.sub.d, y.sub.d) in the progression of the scan through the display area is mapped back incrementally into the corresponding point (x.sub.p, y.sub.p) of the stored datum-attitude map, through a transformation in rotation dependent on the bank angle .phi.. Computation of x.sub.p involves summation of discrete signals representative of x.sub.d cos.phi.