It has to show input and output at the same time (or at least full input), be ergonomic (backlight, nice keys) and not looking childish.
Right now I’m borrowing my SwissMicro RPN which is awesome gadget but outside of complete overkill - its not backlighted display is hard to read.
Context is that the kid has very short working memory. Whereas they understand the concepts really well (I help with tutoring) due to frequent mistakes and forgetting numbers mid-flight the grades are awful which negatively impacts attitude etc.
I noticed positive impact with calculator because not only they start to memorize some basic calculations, they also start to feel general result correctness based on those visual inputs.
As mentioned before - SwissMicro works but maybe there’s something with backlight and not RPN based. It has to be calculator not an app because I hope to convince school to let them used daily.