The Surface Book pen has these functions: 1 - Click the eraser button to take a screen shot via OneNote 2 - Write with the pen nub. Pressure sensitivity greatly improved over Surface Pro 3 pen 3 - Erase by turning the pen around and touching the eraser on the screen. No button pressing necessary. 4 - Hold the eraser button for more than 1 second to open Cortana's search window, rather than speaking, "Hey Cortana". Better in public places.