For any given search the user can type a few words, click on a few results, and going back to the search results until he finds what he wants. He can also chan

For any given search the user can type a few words, click on a few results, and going back to the search results until he finds what he wants. He can also change the words in the search in the process. This last click when the user stops searching is, for this particular user, the most relevant result for any of the search strings he has used. I don't know any search engine that uses this data.