A while ago, I mentioned that Google couldn't do basic subtraction, well a new dynamic online calculator, Calcr, suffers from the same problem.
Once again, enter
1 - 0.9 - 0.1 and press enter. Not the answer you were expecting, is it? (Screenshot for the archives).
If you're curious, Google can now do this simple calculation.
Update: Calcr are even kind enough to suggest another tool - Calcoolate, but it too suffers from the same problem. (Screenshot for the archives).