Hi Kino,
This is from the BTZS.org site and is Phil Davis explanation of the differences.
"Aside from numerous detail changes, most of which you probably won't be aware of unless you compare the editions side-by-side, the differences are additional appendix items ("tools" to aid in curve analysis, and a template for constructing a PowerDial), corrections in some of the "useful equations," and a new chapter on "Gradation," which I think is fairly important"
--John