Daniel Senften

Relive the most iconic programmable calculator ever made. This is a faithful behavioral emulation of the HP-41C, HP-41CV, and HP-41CX — the RPN powerhouse that engineers, scientists, and space missions trusted for decades.

Every keystroke, every register, every quirk of stack-lift behavior has been carefully reproduced from the original Owner's Manuals. If you learned on an HP-41, this will feel like coming home. If you're discovering RPN for the first time, you're in for the most elegant way to calculate ever designed.

REVERSE POLISH NOTATION (RPN)
Enter numbers the way the pros do. The four-level operational stack (X, Y, Z, T) lets you evaluate complex expressions without a single parenthesis. Fast, fluid, and unbelievably efficient once it clicks.

FULLY PROGRAMMABLE
Write, run, and step through your own keystroke programs. Single-step (SST) and back-step (BST) navigation, labels, flags, and the authentic ISG/DSE loop counters are all here — just like the hardware.

EXTENDED MEMORY (HP-41CX)
Store programs and data far beyond the built-in registers. EMDIR, EMROOM, SAVEP, GETP, SAVED, GETD and more give you up to 600 registers of fully-expanded Extended Memory to work with.

CLASSIC PLUG-IN MODULES
Load the application packs that made the HP-41 a legend:
• Math Pac — advanced mathematics and matrix operations
• Stat Pac — statistics and data analysis
• Time Module — clock, alarms, and date arithmetic
• Advantage Pac — TVM finance, equation solving, numerical integration, and matrix math

KEYBOARD-FAITHFUL ENTRY
The full HP-41 keyboard, including the blue-letter ALPHA register and the SHIFT key, works exactly as it should. Type function names, run built-in commands, and explore over 350 documented functions.

BUILT FOR iOS
Designed to fit any iPhone screen edge-to-edge, with safe-area awareness and a clean, distraction-free layout. An on-screen help overlay lets you browse every shortcut and tap any function to run it instantly.

SAVE AND RESTORE
Your calculator state — stack, registers, programs, and Extended Memory — is preserved automatically, so you can pick up exactly where you left off.

A LABOR OF LOVE
This emulator was built for accuracy first. Numerical results are validated against the original HP algorithms, not approximated. It's the HP-41 you remember, with the fidelity it deserves.

Whether you're an engineer who never let go of RPN, a collector who loves vintage computing, a student learning numerical methods, or just curious about a piece of computing history — download it and start keying in.

ENTER your first number. Press ENTER. Welcome back to the stack.