An RPN calculator uses reverse Polish notation, where you enter the numbers first and the operator last. Instead of typing 2 + 3, you enter 2 3 +. The calculator keeps intermediate values in a stack, a last-in, first-out structure that makes multi-step calculations efficient for trained users.
In cyber security, RPN calculators matter less as a threat and more as a reminder that interface design affects mistakes. Security work often involves consoles, admin tools, and embedded devices where a wrong input order can change a result or a configuration value. Attackers may exploit unfamiliar workflows to increase operator error, while defenders use clear prompts, validation, and training to reduce those errors. RPN is a good example of a compact interface that works well when users understand its rules.