All the functions, great interface!
This calculator raises the standard for what it means to be an iPad calculator. The intuitive interaction with the display and the history bar really take advantage of the touch screen in a way that is just impossible on a regular calculator.
On top of all that, it's a great combination of a scientific mode for students or engineery folk with a nice non-scary (aka basic) mode for everyday use. To switch between modes, just rotate.
You might notice there are no M+, MC, MR buttons here - because those buttons become obsolete with the history bar. The app automatically saves all your recent computations (both input and output), so there's no need for special buttons. Instead of one saved number, you have as many as you want, automatically!