Im also new and asked the same question about PAX.
In a nut shell it's a national handicap index. From my understanding it is adjusted either at the end or sometime during the year. For us "lightly Modified" CAM-T (me) guys we are racing all the heavy hitting CAM-T's across the country so our index will never be soft. Like an NHRA stock racer having HP added to there car.
here are my results for all runs (and everybody else) CAM-T 17
https://axwaresystems.com/axorm/file...-feb15_fin.htm
and heres my PAX time,
https://axwaresystems.com/axorm/file...-feb15_pax.htm
If you register, its free, for AXWARESYSTEMS.COM you can get all the results for any weekend and see where you are against others in your class by looking at PAX times.
Sense all the courses are different you can get an idea how others are doing in your class.