With the introduction of the World Handicap System, the way that the amount of shots given or received and the way it is calculated has changed.
With these new handicap inovations, there are a lot or theories about how this should be calculated, but this is the correct way for 4BBB matches and the way all Avalon match handicap difference will be calculated .
All players will find their course handicap from the course calculation chart and find 90% of that handicap. The lowest handicap player will then give the full difference to the higher handicap players.
Here is a link to a handy calculator to help make things easier, (Thanks to Keith Wiggins for this)