This seems to be an expression mode calculator. It simply calculates the result of an expression, which makes it like the other 999 calculators in the Play Store.
Classic algebraic calculators are able to to things like:
57 x = (displays the result of 57x57)
3 = (repeats the multiplication and displays 57x3)
[+/-] MS (inverts the result and stores it in the memory without resetting the previous operation)
7 = (repeats the multiplication for 7 and displays 57x7)
7 [1/x] = (repeats the multiplication for 1/7, displays 57/7)
It doesn't have to be basic arithmetic, this way you can do complex numbers, trigonometry, stats, financial calculations, integrals, ODEs etc. Just have a way to juggle operands and inverse operators, and some quick registers/variables one keypress away (see the classic MS/MR mechanism or the stack in RPN). RPN calculators can often be more efficient, although at the cost of some entry barrier.
That's what you do with the classic calculators. Often, you are not even directly calculating things, you're augmenting your intuition and offloading a part of the problem to quickly explore its space in a few keypresses (what if?..), give a guesstimate, and do some sanity checks on whether you're in the right ballpark, all at the same time. Graphing, dimensional analysis in physics, error propagation help a lot in detecting bullshit in your estimates as quickly as possible. If you're also familiar with numerical methods, you can do miracles at the speed of thought. Slide rules were a lot like that as well.
People who do this might not be your target audience, though.
Classic algebraic calculators are able to to things like:
It doesn't have to be basic arithmetic, this way you can do complex numbers, trigonometry, stats, financial calculations, integrals, ODEs etc. Just have a way to juggle operands and inverse operators, and some quick registers/variables one keypress away (see the classic MS/MR mechanism or the stack in RPN). RPN calculators can often be more efficient, although at the cost of some entry barrier.That's what you do with the classic calculators. Often, you are not even directly calculating things, you're augmenting your intuition and offloading a part of the problem to quickly explore its space in a few keypresses (what if?..), give a guesstimate, and do some sanity checks on whether you're in the right ballpark, all at the same time. Graphing, dimensional analysis in physics, error propagation help a lot in detecting bullshit in your estimates as quickly as possible. If you're also familiar with numerical methods, you can do miracles at the speed of thought. Slide rules were a lot like that as well.
People who do this might not be your target audience, though.