By 1960, using the data developed through the Harkness Rating System, Elo developed his own formula which had a sound statistical basis and constituted an improvement on the Harkness System.
Do 1960., koristeći podatke razvijene kroz Harknessov rejting sustav, Elo je razvio svoju vlastitu formulu koja je imala dobru statističku osnovu i predstavljala poboljšanje Harknessova sustava.