Simplify the following text for a Grade 4 native English-speaking person.
Original: Aaron Rodgers currently holds the NFL record for the highest career passer rating for any player with at least 1,500 attempts , with a mark of 98.4 . The highest passer rating for a complete season is 121.1 set by Peyton Manning in 2004 ( Manning also has completed four games with a perfect passer rating , another NFL record ) .
Simplified: Math is used to get the passer rating .