Similarly, I still have my HP-42s but I usually use Free42[0] on my phone and tablet. They also have it for desktops. It's great if you like RPN calculators. Or if anyone wants to learn about them, you can use that program and follow along with the original manual(s)[1]. It's nice to be able to handle the order of operations without parentheses.

[0] https://thomasokken.com/free42/ I should send them a donation.

[1] https://literature.hpcalc.org/community/hp42s-om-en.pdf followed by https://literature.hpcalc.org/community/hp42s-prog-en.pdf