I still have mine and the user manual sits on a shelf in my basement. I bought mine in a private deal from a guy whose father was a distributor. Cost me $110 in 1984. It allowed me to invert a 4x4 matrix, thereby earning me an A in my power engineering class. I programmed a sinc function to the amazement of my linear systems instructor. And I programmed complex multiplication and division routines. This was pretty cutting edge back in the day, long before mathcad.