How does a search engine measure its own relevance?

If a search engine makes adjustments at its ranking, analysis or Crawling algorithms, which concern a substantial portion of the total volume of all inquiries in the result, one asks oneself nevertheless occasionally: " from where those want to actually know, what is relevant? " now, which is expressed short answer in it: " you [...]

http://internet-news.find-best.biz/2012/05/08/how-does-a-search-engine-measure-its-own-relevance/