Do-Nothing Machine

The Trammel of Archimedes is a device used to trace an elliptical path. It is sometimes made as a novelty and called a "do-nothing machine" or a "smoke grinder." It is extremely easy to print and assemble but hard to put down.

Wikipedia has an awesome .gif of it in action
http://upload.wikimedia.org/wikipedia/commons/9/9f/Trammel_of_Archimedes_Large.gif

The arm could be made more complex, to add a handle or pen holder, but my aim was simplicity. I didn't want to distract from the motion of the device.

Edit: Base-V2. Made some slight changes to the base. Fillets on some of the external faces to get rid of the sharp edges and smoothed out the internal sharp edge the slider would occasionally hit. This should give a smoother motion.