Obviously everyone's needs are different, but what I want from a modern engineering calculator (which I use constantly) is quick calculation of simple things. Anything more complex/verifiable than napkin math, and I'll just use something more serious like Python/Julia, Matlab, any CAS, or whatever engineering/math software I have at my disposal.
So for me, a proper calculator, a tool you master to augment your napkin math, should focus on this:
- Keyboard. Absolutely lowest number of keypresses to enter the problem; the thing that is totally lacking in most non-classic calculators. I can't stress this enough. I should be able to enter all those sophisticated functions without typing their full name and parens. Simple ODEs/integrals should be at my fingertips. I should be able to quickly repeat binary operators for a different argument, and 1/x anything I have on the screen without breaking the flow (on-the-fly calculation often conflicts with that). And many more tricks classic calculators had, which are missing from most modern apps.
- Startup time. It should pop up in less than 100ms. Modern phones and computers are very good at that, but apps sometimes aren't.
- Correctness! It sounds silly, but you can't trust most math applications out there, calculators are surprisingly unreliable, even for simple arithmetic and trigonometry calculations. What math libraries did you use? Or why should I trust your results in general?
So for me, a proper calculator, a tool you master to augment your napkin math, should focus on this:
- Keyboard. Absolutely lowest number of keypresses to enter the problem; the thing that is totally lacking in most non-classic calculators. I can't stress this enough. I should be able to enter all those sophisticated functions without typing their full name and parens. Simple ODEs/integrals should be at my fingertips. I should be able to quickly repeat binary operators for a different argument, and 1/x anything I have on the screen without breaking the flow (on-the-fly calculation often conflicts with that). And many more tricks classic calculators had, which are missing from most modern apps.
- Startup time. It should pop up in less than 100ms. Modern phones and computers are very good at that, but apps sometimes aren't.
- Correctness! It sounds silly, but you can't trust most math applications out there, calculators are surprisingly unreliable, even for simple arithmetic and trigonometry calculations. What math libraries did you use? Or why should I trust your results in general?