I don't go this far back but I do have fond memories of the Casio Fx 501P (I think that was the number) that I bought in 1980. I agonised long and hard over the decision whether to go for that or the 502P (128 program steps versus 256 steps) but my poor student status made the decision for me. It was a beautiful thing and much much cheaper than HP or TI competitors. I fondly remember conceiving and implementing my first program, of any kind, on that thing. It was a dominoes game, and the "AI" worked by maximising the standard deviation (spread) of the tile values left in your hand to try and avoid being left without a play. Standard deviation was one of the built in functions. Man that was a lovely little machine.