iPhone Screenshots


Free42 is a re-implementation of the HP-42S calculator and the HP-82240 printer.
It is a complete rewrite, not using any HP code, and it does not require an HP-42S ROM image.
Free42 is an Open Source project. The executables and source code are released under the terms of the GNU General Public License, version 2.
All third-party code used in Free42 is either in the public domain, or licensed under terms compatible with GPLv2, or used with the authors' permission.

What’s New

Version 2.0.24g

Enabled non-integral display scaling.

Added setting in Preferences to choose whether to stretch skins to fill the screen, or to stretch them only to fill the available width, while maintaining their original aspect ratio.

Implemented support for landscape orientation.

Fixed alignment of "Done" buttons.

Ratings and Reviews

4.8 out of 5
92 Ratings
92 Ratings
Tyyp ,


I believe the HP 42s was the best scientific calculator ever made. And this APP is a fantastic representation of it. If you appreciate the benefits of RPN logic and a calculator that has all the capabilities appropriate for a hand held device, you will enjoy this APP. I have been using the APP for more than a year. The transition from the calculator to the APP was seamless. While there are some minor differences necessitated by the the smartphone platform, they are essentially inconsequential. And the APP has a few major advantages over the calculator such as not loosing programs when the batteries run down.

And the developer has been great. Miscellaneous enhancements and updates required by iOS revisions are very timely and bug free.

I write very few reviews and only when the product is either very good or very bad. If you are looking for a RPN calculator, do yourself a favor and get this APP.

Atlanta Traveller ,

Double love for this app!

My wife and I are both educated as engineers. She got me hooked on RPN after I stubbornly stuck to TI and AOS through undergrad. Then in grad school I started using her HP and before I knew it I was reprogrammed for RPN. We started buying "his and her" calculators as the physical models wore out. When she was complaining about using her iPhone calculator to balance the check book, I selected this app because we had both owned a 42S along the way and loved them. With this outstanding app, well supported with updates, our favorite calculator never wears out. Five stars and a donation. It's well worth it!

Bubba-007 ,

It’s an ok calculator

This app was just updated 5 days ago but doesn’t utilize the additional screen space on an iphone X. I can’t speak to the 8. This is the only drawback I see, but it is a big one. RPN48 lacks some of the functions and features, but I think it sets the standard for an RPN calculator on a smart phone. I would recommend using all the available screen and make the buttons and legends a little bigger, even if it’s not quite to scale with the actual calculator.


Thomas Okken
9.3 MB

Requires iOS 8.0 or later. Compatible with iPhone, iPad, and iPod touch.



Age Rating
Rated 4+
© 2004-2019 Thomas Okken


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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