This app has a great potential, it is very nice looking - this is very important. It would be great if you could put in "About" some reference to mXparser :-) There is no condition in LICENCE for doing that, but still would be nice to promote mXparser :-) Pls consider.
If you need my feedback on the app - just let me know. I already tested it a bit and you have some issues registered.
It would be better to have automatic clearing of "Error" message, i.e. after "Error" appearance when pressing some other button (i.e. number) you clear the "Error first then start with the number :-)
I notice some features like permutation (nPr), nth root (instead of √) and percentage (%) are missing, but are common in other scientific calculators, in the current version. Please add these features
7 -> long pressing "+" -> gives true -> CLR -> true stays in the upper-right corner -> 254 -> long pressing "+" -> true disappears -> long pressing "+" -> true appears and 254 is not prime
2.3 evaluates to 2,3 as in Poland we use "," to represent decimal fractions (ans this is built in android)). But then "2,3" is not recognized by mXparser as number. You should always keep number in the form of "2.3"