and I take it that you find that strange in some way, yes? It really appears that you guys just don't get it. doubles and singles won't act the same way because they have different numbers of significant digits ("significant bits", actually) so they will have differing rounding errors, so to expect them to behave identically is just silly. It all has to do with the difference between decimal fractions and binary fractions and the fact that computers NEVER have an unlimited number of significant digits.

If computers worked in decimal, they would make the same kind of mistakes, just with different numbers, again because of rounding errors.

Take the simplest imaginable decimal number, 1.0 --- Now you would think, since you think in decimal, that this would have an exact representation in the computer. Well, you would be wrong. The binary fraction that the computer generates has a decimal equivalent of .99999999... or thereabouts, depending on whether you use a single or a double. REMEMBER, I'm talking about floating point numbers, not integers. The integer 1 is prefectly representable in binary, but the floating point number 1.0 is not.

Expressed another way, decimal and binary have a different set of rational numbers. That is, numbers that can be represented by proper fractons in one radix cannot necessarily be expressed as proper fractions in the other radix, and when you add to that the fact that there are a limited number of significant digits (or bits) then you get the results that you are seeing, that you seem to find so puzzling.