How many hops when expressed as %

I recently bought a copy of Mitch Steele's excellent IPA book as reviewed on the Beersmith podcast. I'm really enjoying the book and would like to brew some of the recipes. However, I'm a little confused by the way he expresses the hops in the recipes. For instance in the Goose Island IPA recipe he says: "Using only 100% pellets add 16% of Pilgrim T90 hops at the start of the boil. During the whirlpool add 60% Styrian Goldings and 24% Cascade T45 Pellets". But, ??% of what? The only other mention of any kind of ratio is for dry hopping where it says 0.5lb./bbl

Help please ???

I found this which may help you http://thebrewingnetwork.com/forum/viewtopic.php?f=7&t=29027

Thanks Dazed. That's what I'd come to. The crazy calculation someone suggested there is pretty awesome. I may get a math genius mate of mine to come up with a spread sheet Pity there's not a BeerSmith button for allowing you to change the percentage IBU in the design window in the same way you can adjust the grain by a percentage, That's one to suggest for 2.2. Cheers mate.