For Snell-Hitchcock Scav: The Dark Side of the Quad, in the University of Chicago 2011 Scavenger Hunt. Item 115.

The project is written in Processing, and was designed to be used as an Android app so you could turn the dial with a finger. The interface is designed to resemble a padlock, but I was too tired Saturday at 1AM to figure out the correct behavior for how padlocks actually work, with the direction-changing and so on, and it's too easy to accidentally reverse direction briefly when your finger is the mouse.