FSB Readings a little off..?

[slugzkea]

I own a DFI Lanparty 875-T and whenever I set the FSB in the bios, it is always 1 incriments higher in windows.

 

Example: I'll set the FSB to 250 (4.00ghz) in the BIOS. I boot into windows, CPU-Z reads it as 251FSB (4.02ghz)

 

So I'm a bit confused about that.