From Piotr Gridniew:
PG Calculator is a scientific and financial calculator for Android with customizable user interface. PG Calculator works in Algebraic and RPN modes. PG Calculator allows to use addition, subtraction, multiplication and division, Power and roots, Trigonometric functions, Hyperbolic functions, conversion between binary, octal, hexadecimal, decimal, and scientific (exponential) number formats. There is a library of common mathematical and physical constants which can be used in calculations in both RPN and Algebraic modes. PG Calculator also allows to use user-defined variables in expressions.