The Birdie Challenge is split into divisions within each club to give all players a fair and reasonable chance to win.
The divisions can be thought of along similar lines to your clubs grades but is designed to give your administrator the ability to control the number of players in each division.
Sometimes having divisions with different handicap ranges than that of your clubs grades, allows for divisions of similar numbers providing more fairness in the groupings. This allows your administrator some control to avoid having divisions wildly different numbers.