The Hewlett-Packard HP-35 when it was introduced in 1973 it was a total game changer. It single handedly ended the 342 year reign of the slide rule calculator. I remember it so well, in 1972 in the College bookstore I was looking longingly at slide rules I could not afford. Suddenly here was a Hewlett-Packard HP-35 calculator. it did log, and antilog functions, we didn't have to carry around log and antilog tables anymore. I remember muttering 9 significant digits, 9 significant digits, 9 significant digits. The 1973 HP-35 sold for $395 USD. I remember the envy we felt looking at the engineering students who could afford them walking around with their HP's in leather cases on their belts. The fact they used Reverse Polish Notation was mathematical manna from heaven. By 1980 Slide Rules had all but disappeared.
In the App store all of the classic HP calculators are available. I have all of them loaded most of these were calculators I could never afford. My favorite and the one I mostly use is the HP-45 SD. Interestingly the iPhone 14 ProMax is just about the same size as the actual HP-45. By Emulation these calculators function exactly like the original.
RPN Simulators - Simulations of Hewlett-Packard Calculators for iOS
cuveesoft.ch
This is a screen shot off of my iPhone 14 Pro Max/
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