This is a simple line graph designed to allow investigation of aspects of using d3.js and is used as a teaching aid.
It is the baseline example graph used in the D3 Tips and Tricks book.
Edit: June 2014
I am going through a process of updating the code resources for the book and the latest (but not particularly different) example of this graph is here.
https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js