You have to be a real space nut (like me) to fully appreciate the historic significance of this single sheet of paper, posted recently in a Space History FB group:
It's the list of alarm conditions that could be generated by the Apollo Lunar Module computer. It was provided by Jack Garman, a 24-year-old backroom computer guru in Houston during the Apollo 11 mission. Guidance Officer (GUIDO) Steve Bales had it on his desk during the landing, and it was this that gave him confidence to make the call that the 1201 and 1202 executive overload program alarms were not serious enough to abort the landing. Bales received special commendation by President Nixon as he presented a Group Achievment Award to the whole Mission Management team, but perhaps it was Garman who should have had the recognition — or rather, should ALSO have had recognition. After all, it was Bales on the hot seat as Neil Armstrong radioed "Give us a reading on the 1202 program alarm".
Naturally, there was a great deal of post-mortem analysis of that hairy but ultimately triumphant situation, and a story became current that the computer was overloaded because LM pilot Buzz Aldrin had accidentally turned on the rendezvous radar. So the computer was overloaded because the RVR was uselessly pinging a non-existent target. I plead guilty to having spread that false story myself in something I wrote in 1979, for the tenth anniversary.
The fact is that the RVR was on but NOT by accident. It was standard and correct procedure. The thought was that it was a good idea to have it functioning and warmed up, one less thing to worry about in case of a real abort.
The true cause of the overload was much trickier, and more difficult to diagnose. I'll quote from an article in Ars Technica by Lee Hutchinson, dateline 5th July 2019:
"The LM’s rendezvous radar contained a collection of electronics called the Attitude, Translation, and Control Assembly, or ATCA. The ATCA was responsible for providing an electrical interface whereby the LM’s guidance computer could control the radar’s hardware, and the ATCA was powered by 800Hz, 28-volt alternating current. The guidance computer in turn used a piece of equipment called a Coupling Data Unit, or CDU, to read the orientation of the radar’s antenna (its shaft and trunnion angles) so that the guidance computer could keep track of where the radar was pointed. The CDUs—there were actually two of them—were also powered by a separate 800Hz, 28-volt AC reference signal."
As Hutchinson goes on to explain, the two separate AC reference sources were not constrained to be in phase with each other, as they really needed to be for the computer to make sense of the data. Their phase relationship depended on the precise instant at which the LM pilot turned on the RVR and set the mode switch to SLEW.
Even more technical detail on the alarms can be read in Tales from the Lunar Module Guidance Computer by Don Eyles, an M.I.T. programmer who designed most of the system.