Each data point is adjusted to account for HN's growth. The adjustment factor is the difference between the most recent quarter's total items (submissions + comments) and the total items in the point's quarter.
So, for example, Q1 2007 had 7,683 total items and Q1 2011 had 311,190 total items. The adjustment factor for data points in Q1 2007 is 40.5 (until Q2 2011 begins, at which point it changes).
A big thanks to retube for the adjustment scheme.
The actual number of mentions is included with each point for reference purposes.
This little ditty wouldn't be possible without a handful of awesome open source projects, including:
CoffeeScript, Node.js, Redis, jQuery, and Highcharts
The site is proudly hosted on Heroku's Cedar Stack with the Redis To Go add-on.