Figure 1. (A) Recently, very large public displays are being installed, like this digital display of 80m length ((c) Deutsche Telekom). This could enable passers-by to read considerable amounts of content while walking. (B) We propose a model for the perception area of content to analyze content legibility on public displays and three techniques (Zoom, Rotate, Translate) to increase the perception area. (C) Screenfinity is a display that tracks users and uses these techniques to enable reading while walking. A lab and a field study show that experts and novices can read while walking, while many novices stop to engage in extensive technology exploration behavior. ABSTRACT We propose and validate a model of the perception area of content on public displays in order to predict from where users can read. From this model, we derive Screenfinity, a technique to rotate, translate, and zoom content in order to enable reading while passing by very large displays. Screen-finity is comfortable to read when close, supports different content for different users, does not waste screen real estate and allows expert passers-by to read content while walking. A laboratory study shows that expert users are able to perceive content when it moves. A field study evaluates the effect of Screenfinity on novice users in an ecologically valid setting. We find (1) first time users can read content without slowing down or stopping; (2) Passers-by stopping did so to explore the technology. Users explore the interaction, the limits of the system, manipulate the technology, and look behind the screen.