As far as I know, the Apollo guidance computer's DSKY (user interface panel) [1] could only display numbers, not letters. In situations where the computer requi

As far as I know, the Apollo guidance computer's DSKY (user interface panel) [1] could only display numbers, not letters. In situations where the computer required confirmation from the crew it would flash 99 in the program display element and wait for the PRO (proceed) key to be pressed. [1] http://en.wikipedia.org/wiki/Apollo_Guidance_Computer#DSKY_interface http://en.wikipedia.org/wiki/Apollo_Guidance_Computer#DSKY_i...