Originally I had been planning to make a calculator with an Arduino and push buttons. However given a few limitations it seemed easier to first make one completely with software and go from there. This python calculator allows you to store value, do trig calculations, use e and pi, as well as your standard calculations. Below is a link to the code in Google Docs. There is an attached file that you need as well to run the program. Download both and put them in the same folder then open and run with idle.

https://docs.google.com/open?id=0B54ZgSAhwvI0ZDBRaEdwQUNfZUU