Manygeese,

I asked this same question quite a long time ago in someone else's post.

For me, class is the consistency factor, that the horse is able to win and win and win etc etc etc. It is measured by past history, as this indicates if it won or not. And one of the best known factors to measure class is the prizemoney it has earned.

Just like Tennis players and Golf players and Race Car drivers and even Chess players.