The manuals found on Bitsavers were a great help, they are very detailed and explain the system well. The original instruction test tapes helped me a lot with

The manuals found on Bitsavers were a great help, they are very detailed and explain the system well. The original instruction test tapes helped me a lot with debugging the various corner cases. For example, the multiply step opcode (MUS) is re-used in later versions which had full hardware multiply (MUL). The backwards compatibility was retained by flipping a switch inside the computer to selecting between MUS and MUL. I had some programs failing mysteriously because of this. There were also various pixel brightness available and after implementing it, I discovered Spacewar actually uses that to make some stars brighter than others. Music playing capability was very advanced for its time (having 4 voices) and after everything was a "silent movie" for a while, there was a rewarding moment when I finally fixed a bug and Mozart started playing from the speakers. A cool machine, very advanced for its time... Cheers!