Figure 5. Illustration of the binary chop algorithm finding the best operating point for an arbitrary assortment of attenuators in the beam. The x-axis represents successive points along the entire automatic brightness control (ABC) curve data set whilst the y-axis shows the image intensifier air kerma rate for the tube potential/tube current combination of the ith point on the curve. Each arrow shows the operating point chosen by successive iterations of the algorithm and the spot represents the tube potential/tube current point that results in the air kerma rate being closest to the desired value.