Facebook defines EdgeRank as: Affinity x Weight x Time Decay. Facebook measures Affinity between Users and Pages by monitoring their interactions. Interactions are objects such as Likes, Comments, Clicks, Shares, Wall Posts, and anything else that Facebook can tangibly measure.
EdgeRank Checker provides complete analytics for Affinity. This is a valuable metric you will not find anywhere else!
The Affinity grade displays the process of understanding these Interactions. Facebook allows us access to analyze Interactions through Comments and Likes. Understanding how users are interacting with your Page can be incredibly powerful.