What's 1 - 1?
1.0 - 1.0 = 0, right?
1. 0 - 0.9- 0.1 still equals 0, correct?
well, don't trust your google calculator too much.
http://www.google.com/search?hl=en&lr=&q=1+-+0.9+-+0.1&btnG=Search
I also tried it with MSN search, and appearantly, they give the same answer.
http://search.msn.com/results.aspx?q=1.0+-+0.9+-+0.1