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dc, perhaps.

Not sure what the parent uses, but emacs has calc, which is a RPN calculator with lots of features (including history and intermediate results) and can be used in the terminal

To be honest, I mostly use a physical calculator (Swissmicros DM41L, which is an HP41CX clone). Second choice is the i41CX+ app on my phone. The HP41 keyboard and operational patterns were etched into my brain at university, since my first engineering calculator was an HP41C.

I have used rpncalc and T_REX (https://isene.org/2021/02/T-REX.html) in the terminal, dc or gforth in a pinch.