In July 2005, there is a patent filed in the US Trademark Office from Monika Henzinger, that states that she has found a way to determine how fresh of your document, that is your web page.
Some search engines are using the last-modified-since in the HTTP header for determining the freshness of the web page, however, this method has an obvious abuse with modification of HTTP header. With these abuse, what Google do is really looking into the modified content of your page, even though it is still a secret of how score it gives to a page in which it is more fresh than the others, obviously, it counts if your site is a forum, otherwise it does not count it is a historial reference only.
Anyway. freshrank is still a secret so far!!!
