Appendix C: Minimum Object Resolution

The amount of data that can be displayed on a screen is determined by the resolution of the screen, measured in pixels. The size of each pixel, however, can vary - and because a mobile device must be portable, the screen can't get much larger than it presently is. As a result, as resolution increases, the size of each pixel decreases. So the problem arises as to how small can a pixel be, and still be visible to the human eye at a reasonable distance (arm's length).

The author presents some equations that are beyond my comprehension: trigonometry based on the angle of view, the sensor dimension, and the focal length. My sense is that this has less value to designing for mobile devices than to designing the mobile devices themselves, so I'm not too intent on pondering the mathematics.