This project has created scientific firmware for the HP-20b and HP-30b business calculators.

The WP 34S turns either of these calculators into a powerful keystroke programmable scientific device. According to our customers, it's the most powerful and fastest RPN scientific pocket calculator ever built.

The WP 34S is alive and stable since 2011. We have succeeded in satisfying the most picky users - read about their experiences on Find the Owner's Manual v3.2 at

In 2014, we've updated the WP 34S to version 3.3. Our customers confirm its documentation is excellent and comprehensive (see feedback); an updated printed edition is available from since June 2016.

We have also produced the WP 31S which is derived from the WP 34S source code. This is an entry-level scientific calculator. Its printed manual is available from

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User Ratings

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User Reviews

  • Absolutely magnificent good work. A perfect calculator project. A briliant idea as well, to replace a half stupid hardware with a big brain transplantation. In this project I can smell the engineering art of HP in the late 70th to 80th. Delivered with a professional documentation, which seems to have the approach to be comprehensive, which is quite impossible in view of the wealth of functionality. And as far as I tried until now, there is no error, no single bug in the software!

  • Works with WINE on Linux!

  • A fantastic resource and powerful tool. With unprecedented accuracy, speed and feature set. The WP-34s extends the RPN model beyond my wildest imaginations while providing ease of use, excellent documentation and frequent updates. For the serious scientific handheld calculator user who preferes RPN, this stands far in advance of any alternative. That it is so inexpensive is just incredible. Well done, gentlemen! Jim Horn, HP RPN daily user since 1975

  • WP-34s: The HP calculator that HP could never build. The current "top of the line" HP scientific-programmable calculator is the HP-35s, which for reasons I won't get into here, is not as good as the calculators HP made during the 1970s and 1980s. With a switch back to in-house calculator development, HP made the HP-20b and HP-30b calculators so that you could flash your own firmware and turn it into whatever you wanted it to be. That's what Walter, Pauli and Marcus have done - borrowed a bit of code from the Open RPN project and with lots of new code, produced the WP-34s firmware which is basically an HP-42s + HP-16c plus a whole lot of new stuff never seen before in an HP calculator. You could get an HP-30b, flash it with the WP-34s frimware, apply a keyboard overlay from Eric, and happily use it as an HP-42s and do all the things you could do with that calculator, and not use half the functionality of the WP-34s. Programs can be written, tested and debugged using Neil's compiler and one of the Pascal's multi-platform emulators of the WP-34s, then transferred to the calculator via the serial cable. Maybe one day HP will build something to match the WP-34s, but for now, it's the greatest HP programmable scientific / computer science calculator ever made!

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Intended Audience

Information Technology, Science/Research, Education, Manufacturing, Engineering, Automotive

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