  We present a conceptual model that describes the effect of pixel size on
target acquisition. We demonstrate the use of our conceptual model by applying
it to predict and explain the results of an experiment to evaluate users'
performance in a target acquisition task involving three distinct display
sizes: standard desktop, small and large displays. The results indicate that
users are fastest on standard desktop displays, undershoots are the most common
error on small displays and overshoots are the most common error on large
displays. We propose heuristics to maintain usability when changing displays.
Finally, we contribute to the growing body of evidence that amplitude does
affect performance in a display-based pointing task.
