1. A computer-implemented method comprising: identifying one or more sessions for a query, each session comprising a chain of respective resources linked to each other and watched by a respective user, each session beginning with a first resource that was identified by a first search result responsive to the query and linked to one or more second resources, wherein each second resource was associated with a different resource in the session by a respective link, and wherein the user visited each second resource by following the links; associating a total of watch times of the respective resources watched in the sessions with the query; calculating one or more watch time signals for the first resource and the query based on the total of watch times associated with the query; after the one or more sessions have ended: receiving the query from a user; obtaining a search result responsive to the query, wherein the search result identifies the first resource and has an associated score S; calculating an updated score S′ based on at least S and a watch time function, the watch time function being a function of the one or more watch time signals; and providing the updated score S′ to a process for ranking search results including the search result.