I'm afraid I have to disagree with you there. The system for calculating the level of a spell is slightly wacky and highly fudged, but it is stated unambiguously in the rulebook. Unfortunately the rulebook is not written to be a reference manual, so you have to read all the relevant sections and work through the examples, but once you know what you're looking for you can find it.
Well, it mostly fixes the broken rule. It's not that bad.
What's that in Geek Code (er, I mean ArM code)? G++++?
By demonstrating, and giving other examples, that it is a simple, self contained system (not a botched fudge or bodge), just not necessarily a familiar one.
The man asked for a detailed explanation in simple language. That means lots of unnecessary extra stuff for those that 'get' it straight away. It also means coming at an explanation from multiple directions in the hope that one of them sticks.
Personally I find it an extremely simple and elegant method that does a great job in achieving the sort of magical balance that makes low level spells easy for any mage, mid level spells harder but achievable and awesome rituals still achievable with experienced PCs. It took me all of 10 seconds to grasp. But I can understand (intellectually at least) that others may have a harder time of it.