This calculator was actually designed for me. I treat myself as the user. And I want to design a solution to meet my needs for a calculator. I want my calculator to look simple but professional. So I only used two main colors in this design, black and blue. This two color give people a feel of reliable and expertise. 

Besides, I have a special need that is I want to be able to see the history when I will deal with a large amount of calculations. So I design it with the function of view the history. Users can use the button "C" to clear all history. To fix mistakes, users can use backward button beside the "equal" button.