I'm being confused by the wording on uspsa classification and the percentages. For easy math lets say you classified at 50% are you as good as half the people shooting uspsa, or are you half as good as the best they know of?
Even that's not quite true... some of the top scores (the "high hit factor") used to calculate your national % on each classifier are based on actual scores from nationals, some are more arbitrary, and some are based on a perfect score (eg fixed-time courses).
It's just a way to divide up the shooters into similar ability groups. Don't read much more into it than that.
Shawn as Ryan said it is based on where you fall from the top shooters.
There is some flaws in the system but it is a decent system.
C class is the biggest by a big margin.
Here is a breakdown for you.