I am still using my old HP45 calculator that I purchased new in 1973 for USD395. (Wiki tells me that in 2017 terms that was the equivalent of USD2178).
It was the first scientific calculator that I had ever heard about, and I had visions of it changing the world.
I can read it in poor light, because unlike modern calculators it has a red LED display.
Apart from its speed advantage, I found that the RPN also had a distinct advantage in a work environment, because nobody ever asked to borrow it more than once.