This is a calculator which uses Reverse Polish Notation, or RPN. A full write-up in Japanese (Google Translate link) carries an impressive level of detail about the project, but in short ...

Design space is proposed by the applicant and ... All three scores are multiplied to provide a risk priority number (RPN) and the RPN scores are then ranked to identify the parameters with a ...

This glorious specimen is an open hardware RPN calculator with more than a nod to the venerable Hewlett Packard HP42 in its design. At its heart is an STM32L476 low-power ARM processor and a Sharp ...