 An Elo rating is a comparative rating only, and is valid only within the rating pool where it was established.Arpad Elo was a master-level chess player and an active participant in the United States Chess Federation (USCF) from its founding in 1939.The USCF used a numerical ratings system, devised by Kenneth Harkness, to allow members to track their individual progress in terms other than tournament wins and losses.