Al Williams writes about the surprising continued availability of Reverse Polish Notation calculators in 2026, despite RPN losing the mass market to algebraic entry decades ago. RPN uses a stack-based system where operators follow their operands, eliminating the need for parentheses or an equals key. Today's options range from the still-sold HP-12C to SwissMicros' modern enthusiast machines, DIY builds on ATmega and ESP32 hardware, and a thriving ecosystem of phone and desktop apps.
- The first RPN calculator was the Friden EC-130 (1964), a 44-pound desktop unit at $2,150 whose CRT displayed all four stack levels simultaneously
- SwissMicros' R47, at ~$300, features an 8-level stack, built-in electrical engineering functions, and firmware still officially in beta
- HP released a native Linux build of HP Prime as a 2019 AppImage, but it predates the Python programming addition; the only way to get Python on Linux is running an older Windows version under Wine with Soda 9 in Bottles, and you must not let it update
- Alex Garza's PAXER kits reproduce HP-15C/16C/41C on ATmega328 for under $100, adding continuous memory, backlight, and real-time clock
- The 10LC turns a ~$50 ESP32-based M5Stack Cardputer into a pocket RPN calculator
- Free42, a clean-room HP-42S implementation by Thomas Okken, runs on Android, iOS, Windows, macOS, and Linux
- The first RPN calculator was the Friden EC-130 (1964), a 44-pound desktop unit at $2,150 whose CRT displayed all four stack levels simultaneously
- SwissMicros' R47, at ~$300, features an 8-level stack, built-in electrical engineering functions, and firmware still officially in beta
- HP released a native Linux build of HP Prime as a 2019 AppImage, but it predates the Python programming addition; the only way to get Python on Linux is running an older Windows version under Wine with Soda 9 in Bottles, and you must not let it update
- Alex Garza's PAXER kits reproduce HP-15C/16C/41C on ATmega328 for under $100, adding continuous memory, backlight, and real-time clock
- The 10LC turns a ~$50 ESP32-based M5Stack Cardputer into a pocket RPN calculator
- Free42, a clean-room HP-42S implementation by Thomas Okken, runs on Android, iOS, Windows, macOS, and Linux
