Compensation and ratings

I work at a regional firm in NY and I was reviewing the PWC compensation thread and was wondering if someone could explain the ratings/levels to me.  I’ve never worked at Big 4 so the A1 to A2 levels don’t mean a lot to me. Is this just going from a first year audit associate to a second year audit associate?  With the ratings, is it better to be a 1 rating or a 3?  At my firm we are rated out of 5 with 5 being the best. I’m trying to see if my compensation is in line with those around me but I can’t follow the ratings well.  I know my raises/bonuses have never been 15-20% (nor will they ever be probably) but I want to get an idea of how my overall compensation compares.