Free42

This is an awesome RPN calculator, and does all the things you need and more.

Yep. Seriously. This is one of the very best calculators available for download on the internet. As a FREE app, perhaps only the Wp-34S and a handful of others come close; and the few that do are almost exclusively based upon ground-breaking machines produced by Hewlett Packard. Highlighting Free42's capabilities could fill a small book - and it's better than the machine it's based upon! Thankfully, manuals, web-sites and forums exist to support this magnificent piece of work, and although exploring the wealth of information is not essential, it is educational and highly rewarding. Different skins are available too. They can be swapped in seconds, even during a calculation. And not only do they alter the appearance; in many cases they make subtle modifications to provide quicker access to various functions. Bottom line: Hundreds of calculators can perform basic arithmetic; but some do a whole lot more…

Simply the best calculator app on the AppStore

What a wonderful surprise to find this. I’ve still got my original HP 42S but now I can use this one when I’m out and about. Thank you!

I love that this app is available on iPhone. It’s have a HP-42s and a DM42 but this is super handy on my phone. The haptic feedback, button press sound and that the buttons move when you press them are all great little touches. If you are familiar with the 42S this is for you. If you are interested in learning to use an RPN programmable calculator this one is very well documented and easy to program so it’s a great place to start. Would be nice to have an additional skin which makes better use of the empty space, and the ability to view all registers etc.

Unbelievable that this implementation of the fabulous HP42s is provided free. Stable, precise, useable and a superb simulation of the original classic calculator.

Just spent a little time with this . Absolutely fantastic. Thanks for developing this and the manual for it. Steve

Respect to Thomas for creating this... and making it free, to boot. Brought back many memories, so much so, in fact, that I decided to spring for a real HP 35S on eBay to replace my stolen 42S! Just one small suggestion that would make this truly awesome: imagine being able to see all five registers – X, Y, Z, T and L on the screen at once...

Respect to Thomas for sharing HP42s with the world. Calc input is fool proof compared to the logic on modern calculators but RPN input will take you about 10 minutes to learn and that puts people off. You don't need brackets and equals. HP42s is so good that a working example 25 years old is worth £200. I got mine in 1990 use it all the time. Try it and see.

My HP42 gave up the ghost a couple of weeks ago and I felt lost without it. The replacement non-RPN Casio just didn't hit the mark. This app was a real saviour, I love it. Well done and thanks for the App.