This reminds me of the first time I tried to use an HP RPN calculator. It was circa 1972, and I was taking undergraduate courses at Rice University. I showed up for my physics final only to realize Id forgotten my calculator, a TI SR-10 - an early replacement for the slide rule, the basic 4 functions, square root, inverse and squared added. There were lots of calculations to do on these tests, and it was gonna be a slog without a calculator. The TA proctoring the exam had his calculator on his desk, an HP35, but he wasn't using it, so I asked him if I could borrow it. With a sly grin he asked "ever used an HP calculator before"? I said, no I hadn't, but, how different could it be, a calculator's a calculator, isn't it? "Sure", he agreed, and pushed it over to me with a smile.
So went my first encounter with RPN, which I had never heard of before....I didn't do at all well on that exam. Oddly enough, years later when I got an HP16 for my programming job, I felt in love with RPN, and prefer it to algebraic entry calculators to this day.