Bi-tran Six, Used one in 1970-71 10th grade computer science class. I think it could do math with a result up to 31. I remember something about a bit being used to designate negative number. And some functions like greater-than and/or equal-to. My teacher used it to demontrate programing in machine language. I remember the pull out core memory boards and it was on a rolling platform. Pretty big for what it's capable of. Wow, that's a long time back.