'413' is an AGS address and has been a topic of considerable interest to Journal Contributors Marv Hein and Frank O'Brien. Frank supplied the following description.
O'Brien - "(The AGS is) a wonderful machine. If you have done any work on a computer that just has a switch register and display (such as an IMSAI, ALTAIR or one of my favorites, the KIM-1), you'd be comfortable with the AGS."
"The way the AGS operated is that you had only an address and data display, 0-9 keypad, a Clear button, plus +/-, Enter and Readout. That's it. The ultimate in simple interfaces! How the AGS was operated was to press Clear, then a memory address. On a 5-octal character display, you got what was stored in that location. To change it, you typed a +/-, followed by 5 characters. Pressing Enter stored the value directly into memory. What you hear is the checklist item noted as: 413+10000. The key sequence is Clear, 413, Enter, +10000, Enter."
"Address 413 contains the variable that indicates that the LM has landed - so any abort will be from the surface - which further tells the AGS to save the attitude information from its gyros. These gyros were 'strap-down' types, which means that they had a fixed orientation with respect to the LM body. They also had a nasty habit of drifting quite a bit. So, as soon as they landed, the AGS was to 'lock in', if you will, the attitude the LM was in. If the PGNS died - and it was the PGNS that oriented and re-aligned the AGS - at least they would have some approximate attitude information to abort with."