Crash,

As I said, I'm not having a go at you or this system. It's just that I've seen many systems that use barriers 1-7 and it just doesn't seem to make much sense to me. Why should barrier 7 be successful and barrier 8 not? I suppose if you're making a rule regarding barriers, you have to have a cutoff point somewhere. I just can't quite work out why it's 7.

If someone can reproduce some figures regarding barriers, it would be appreciated.