That's the class designation for the PAX class. Many clubs, SCCA-OR among them, have a class where the more experienced drivers compete against each other, rather than against drivers with similar cars. They compare their times by applying the PAX index, an approximation of the relative performance capabilities of the different classes.

Steve

 

Steve, I know what PAXing is
I wish they PAXed cars here. Instead, both local Porsche series pile all non-P-cars into a single class that is not PAXed.