Hansell, Saul (June 3, 2007). "Google Keeps Tweaking Its Search Engine" . New York Times . http://www.nytimes.com/2007/06/03/business/yourmoney/03google.html . Retrieved June 6, 2007 .   ^ Danny Sullivan (September 29, 2005). "Rundown On Search Ranking Factors" . Search Engine Watch . http://blog.searchenginewatch.com/blog/050929-072711 . Retrieved May 8, 2007 .   ^ "Search Engine Ranking