Search rankings are passively assessed and only for Google search referrers. Google believes very strongly in search privacy but for some reason they "leak" the ranking of a search result in the referrer when a visitor clicks on it. We monitor for this leaked ranking and log it for each person who clicks through. The ranking you see is the average of all provided rankings for each search phrase.

The ranking for a particular search is unique for each visitor because of locale and other preferences they have setup in their Google account. Hence, we average all clickthrus together to give you a general idea of how well your site ranks for any given search, but it's just that: a general idea.

In the future we want to add "scraping" functionality for a set of pre-defined searches you care about, so we can track them across multiple search engines. But for now, we rely on the passive system and hence can only report on the data that Google provides us, as they are the only one that does that.