There is probably a calculator built-in to your Operating System. For Windows, press startup (Bottom left) and then type calculator in the window ("Search programs and files"). Macs probably also have them.
Google also provides one. Just type "calculator" and woosh - you have one.
Google can also be used to plot functions. Just type sin(x)/x in the Google search window- it's a cool function (sinc(x)) which has MANY applications in physics (RF). Virtually any function of x can be plotted. Just type the equation - ie: x^3 +12x^2
-4x +1 and hit enter - wooosh!!!
Handheld calculators are already obsolete ;-)