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 ...

Holding Perkebunan Nusantara PTPN III (Persero), PT Riset Perkebunan Nusantara (PT RPN), dan Palm Oil Agribusiness Strategic Policy Institute (PASPI) menyelenggarakan Seminar Nasional “Peran ...

Why reach for a bland, commercially available calculator when you be using a model that employs RPN (Reverse Polish Notation) in its calculations and be a custom build all at the same time?