That's just it, they're not trimming every horse the same. They're not even trimming every foot on the same horse the same. It's all guided by the conformation and landmarks of each individual foot. You could even have a different sized shoe on each foot, or different angles for each foot, if that's what the horse needed. You're not shooting for cookie-cutter feet.
Oh, well that's interesting.
I really need to get the book:)
Becky