Free42

Thomas Okken

About this app

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.

Ratings and reviews

This RPN calculator is delightful to use. It is packed with many advanced features that are intuitive and work well together. I especially like that variables can be given names, custom menu slots are available, and you can write programs to add functionality or speed up a calculation you do often. For those new to the app, I would recommend enabling big stack mode (NSTK) to avoid the limitations of a 4 level stack.

Incredible RPN calculator! If you like HP calculators, this is flat out amazing! It has the same layout as the original HP-42s. It even runs the same programs -- but much faster than the original! There's a "haptic feedback" option which feels something like the actual HP key clicks. There are other layouts if you like a horizontal layout. The settings screen is accessible if you touch the calculator display.

I still have two HP42s, one for my office at work, one for my office at home, both in a drawer. Free42 now resides on my phone and computers. It is a perfect emulation with some significant advantages in stack height and memory. I occasionally miss the HP's programmability, but usually just turn to a spread sheet for highly repetitive calculations or more specialized apps or programs for more challenging work.

What’s new

Fix for hang during audio playback.