This online calculator web app has the standard four functions for addition, subtraction, division and multiplication.
It also offers some of these functions:
sqrt = square root: take the square root of the displayed value and display it
sq = square: square the displayed value and display it
( and ) = parentheses
+/- = plus/minus: change the sign of the displayed value from positive to negative or vice versa
cos = cosine
sin = sine
tan = tangent
clear = clear all and start a new operation
back = delete last digit or symbol