There is a rule in programming that says that if you think Select is wrong then you are wrong.
Excel is definitely not getting the maths wrong, its simply impossible. I suspect the number is formatted to less decimal places or something else is off.
i7 3930k @4.4, 2xMSI GTX 680, 16 4x4 GB Corsair 2133 RAM, Crucial m4 500GBXonar D2X. All custom watercooled by 2x MCR 320 and 1 MCR 480
Zowie Evo CL EC2, Corsair K70, Benq XL2411T