-Does it calculates natural logarithmes? (ln(x))
-Does it calculates limits? (
http://en.wikipedia.org/wiki/Limit_(mathematics))
-Does it calculates sin, cos, tan?
I think that a calculator called advanced if it will can calculate those functions.
Also add support for mathematical processes like ((20^3)/(10^(-5)))*(25^(31/17)) and the user will write something like that, and the calculator will print the result.
Those are some suggestions to you.
Good job anyway ;)