I believe that one difference between AI.23 and AI.23B was that in the former the pilot used the CRT to acquire the target and then switched to the PAS (which provided steering and range marks) for the final attack. There were a number of criticisms of the PAS, and also of the need for the pilot to change from “head down” to “head up” during the final stage of the attack. Hence in AI.23B the entire attack was carried out “head down” using the CRT.