Write the equation on the screen, the app uses handwriting recognition to translate it, and up pops the answer.
The following examples were all generated on an iPhone 5. The diagrams are the output from the calculation (easily stored as photographs or emailed). Landscape orientation is much easier to use than portrait orientation.
The following figures show is a sequence of calculations. The equation is altered by adding extra calculations to the equation.
Cool. Fast. And big attention getter in a meeting. You too can be the coolest nerd.