My friend at mesa who was there for 6 years said he NEVER had to use the 7347 (or whatever its called) rule. Or ever have to derive mins. It was a very hard concept to grasp in my initial new hire training, and I still dont have a good understanding on it lol. I think the "when do we need a second alternate, how to derive mins, 74347 rule" and all that gets people a lot of stress in studying.