http://code.tutsplus.com/tutorials/android-user-interface-design-creating-a-numeric-keypad-with-gridlayout--mobile-8677


http://www.fampennings.nl/maarten/android/09keyboard/index.htm


http://stackoverflow.com/questions/18033996/how-to-make-my-toy-android-calculator-ui-fits-with-the-device-screen


http://stackoverflow.com/questions/6893147/android-custom-dialog-calculator-laying-out-different-on-android-2-2-1-and-2-3


http://cyrilmottier.com/2010/12/13/adding-quickactions-to-your-app-with-greendroid/


http://stackoverflow.com/questions/22779351/save-the-number-in-the-list-through-edit-box-but-it-will-show-same-number-in-the