Back in 1975 (I think) I bought a plastic slide rule to compare my newly discovered abilities on it against the calculator we had in the house. It was a clunky thing that could do basic arithmetic only. It might have been accurate to more decimal places, but I could do logs and more esoteric calculations much faster on the slide rule than I could with that calculator.
That all changed though at the end of 1977, when I got my first portable calculator as a Christmas gift: the Texas Instruments SR51-II. It wasn't as cool as my friends' HPs with RPN, though. Still, I was fascinated with the thing, and would play with numbers for hours. One of the funnest (yes, funnest) things I remember doing was calculating the distance to a star using parallaxes. What. A. Nerd. I still remember that the highest number I could quickly generate was 69!. Little did I know at that age the magic of that particular number...
At any rate, for your viewing pleasure, the portable computing tools of the last part of the 1940s.