I don't often promote apps but yesterday I came across an app for my iPad that I just love. MyScript Calculator was featured in the Apple App Store and it's free and looks fun so I installed it. It's very simple; you write a mathematical formula on the iPad's screen, just as you would with a pencil and paper, and it converts your handwriting into digital form and does the calculation for you. Any mistakes you (or it) makes can be easily undone. Watch the video below to see how it works. It's available on Android as well.