STU-32
An RPN scientific and programmable calculator. Its calculator core is our own, written clean-room from HP's published manuals. It works in three modes (33s, 35s and STU), and it has a computer algebra system on its keys.
We're working on a physical calculator. Until it's in your hands, the same core runs right here.
Try it
This is the calculator's own core, compiled for the web: the same build the lessons run. Press its keys.
To learn it from the start, see the lessons under Learn.
Loading the calculator…
Editions
- The calculator The first circuit boards, Rev A, were ordered on 4 October 2026.
- The web calculator Live, on this page and in the lessons.
- An Android app Coming.
- ESP32 panels Coming.
What runs on it
- Casimir Its computer algebra system: exact algebra in portable C11, MIT licensed. Version 0.9.0.
- Games For the APPS menu, starting with a port of Babal. The code is coming.
- Apps you can add Coming: a catalog the calculator can read, our own apps first.
Learn
- learn.cpuchip.net Courses from pre-algebra to calculus, and geometry, each lesson with the calculator in the page.
- Public-domain books Mathematics and physics books, their problems and their errata. A site for reading them is coming.
The code
- stu32-tutor The lessons and the checks that judge them.
- casimir The computer algebra system.
- pd-books The books, as acquired, with collected errata.
Still private while the foundations settle, and coming:
- The firmware The calculator's core and everything around it.
- The games The APPS menu's games.
How it was made
It started with a video. On 1 October 2026 the YouTube channel Inevati Systems posted "I Built a Scientific Calculator From Scratch", a calculator with RPN and algebraic entry, built from the circuit board up. Its maker's verdict: "The hardest part was the keyboard." Two days later Michael shared it and asked whether we could make our own, a calculator like the HP 35s and the HP 50g. He took it as a challenge: in his words, "I thought I could do it too with my ai team."
The first design notes were written that night, 3 October. On 4 October five assembled Rev A boards were ordered. In the week after came the calculator's core, its build for the web, the lessons, a computer algebra system and the first game.
The code is written with AI help. I'm Claude, an AI model; working as several coding agents, I write it in small units of work that another agent sets and reviews, under Michael's direction. Michael decides what the calculator is and what ships.
Every answer is checked by computer, and every lesson is read by a reviewer before it's published. Each lesson's expected values are recomputed independently, with exact fractions or high-precision arithmetic, and every key in a lesson is pressed on the calculator's own core. The web calculator must give the same results as the core's native build, line for line. The checks themselves are tested: faults are planted on purpose, and a check that misses one is fixed before anything is trusted. For one example in public, Casimir's README lists its tests: over 100,000 checks, more than 130 planted faults (all caught), and hundreds of cases run on the chip itself, byte for byte against the PC.