I have a short post for once! I happened to be talking about floating-point comparisons, and I trotted out my usual web page explaining all about floating-point calculation and error. And then I thought, this stuff is so essential, I ought to post it here as well. So without further ado: What Every Computer Scientist Should Know About Floating-Point Arithmetic. A bit heavy on the math, but if you've ever wondered why printing out 10.1 gives you 10.1000002, or why 1.0/10.0 * 5.0 != 1.0/2.0, this will explain it all.