Put the processor into single instruction mode, set SR with some value, click "Load Add," then "Exam." You get some value on MB, as the 1970 Small Computer Handbook says you should. But load the address and exam again, and you get a *different* value in MB!

Furthermore, poking around with the "e" command at the SIMH prompt gives different values still. Poking a value in with a "d" command and then trying to Exam it via the front panel doesn't work.

Is this entirely broken? It used to work. Apparently we're going to have to go bisecting. To whoever does this checking: be aware that you can say "make bin/pidp8-sim", which should avoid the need to rebuild the media on each bisect step.