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The power of RPN

A quick journey through pocket calculators and my personal collection

Scritto da Silicon_Simon.
Domenica 16 Novembre 2025, 3:54 pm. Tag usati: calculator, fun, hp, retrocomputing, rpn

Reverse Polish Notation (RPN) stands out as one of the most efficient methods for mathematical calculations, especially for technical professionals and enthusiasts like me. Unlike algebraic entry, RPN allows users to enter operands and operators in a sequence that eliminates the need for parentheses and reduces keystrokes, a feature that makes it extremely fast and direct for complex computations and algorithms.​

If you add these premises to my more-than-two-decades long passion for retrocomputing, you can consciously enter my world!

RPN traces its roots to the logical systems proposed by Polish mathematician Jan Łukasiewicz in 1924: actually he formalized it more than a “prefix” (operators then operands), later “postfix” by the Australian philosopher and computer scientist Charles L. Hamblin, who switched operators after the operands in his notation. Hewlett-Packard (HP) played a pivotal role in popularizing RPN entry systems during the 1970s and 1980s. HP's implementation of RPN, relying on stack-based logic, significantly streamlined calculations for engineers and scientists. Legendary models like the HP-35 and HP-9100 pioneered RPN handheld devices, cementing its reputation among professionals.

For an in-depth historical perspective, see this nice HP Museum's comprehensive post, The Evolution of RPN & Numeric Entry.

My small RPN Calculator Collection

I've been fascinated by the RPN's elegance since my early university days, when I, a young engineer-wannabe, got my hands on my first wonderful HP 48G, lost in time but soon replaced by many other RPN devices over the years.

Many engineers used RPN calculators during their formative years in university or early careers. These machines represent a tangible link to our professional development and problem-solving journey. Moreover, vintage RPN calculators were engineered as precision instruments, not disposable consumer products. Built with robust materials and meticulous craftsmanship, many units from the 1970s-80s still function perfectly today. The tactile feedback of the keys, especially the famous "click" of HP series, is unmatched by modern devices. This contrasts sharply with today's planned obsolescence.

There's a vibrant community of enthusiasts sharing knowledge, repair techniques, programs, and stories on forums like hpmuseum.org. This creates a sense of belonging among like-minded problem-solvers. Restoring vintage calculators combines electronics skills, detective work, and historical preservation. It's intellectually satisfying to bring a 40-year-old machine back to life.

Below is a presentation of my RPN calculator collection, listed by their introduction date for each model. The collection highlights iconic HP calculators, which have served generations of engineers, scientists, and financial professionals.   

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