recipe disagreements

[Radler]

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I was wondering if anybody can tell me why I get such different results on recipes when using two different "methods". When I calculate what the OG and IBU etc will be using tastybrew.com it comes out very differently than if I use calculations from John Palmer's "How to Brew". I trust both of these but they can't be so different and both right. Example is my last beer: 5.75 lbs of extract gave me a 1.046 OG with Palmer and a 1.055 on tastybrew, when I actually brewed it and neasured it, tasty brew was right, but Palner doesn't have a book by being wrong. Any ideas folks?

Rad

[Steve973]

Being that specific gravity measures the percentage by which a solution differs from water in weight by volume, the Palmer book differs from your online source in less than one percent. One says that, by volume, your wort will be 5.5 percent heavier than water, and the other claims 4.6 percent. That's not too bad. Besides, I'm sure that not every extract will not add precisely the same amoung of SG points by weight to your wort. I'd imagine that, sometimes, Palmer will be more correct, and the website will be correct at other times.