The first new pricing metric was based on “click-through rates,” or how many times a user clicks on an ad through to the advertiser’s web page, rather than pricing based on the number of views that an ad receives. The click-through was interpreted as a signal of relevance and therefore a measure of successful targeting, operational results that derive from and reflect the value of behavioral surplus.

Shoshana Zuboff, The Age of Surveillance Cap…, loc. 258