Strange problem with adjusting FSB

[CR0W M@GN3T]

I am using a ECS BLACK SERIES A780GM-A motherboard and although its limited, overclocking is possible.

The problem is that when I set a FSB, CPU-Z indicates that the FSB is not changing on a 1:1 ratio.
For example: I set the FSB to 209 and CPU-Z says that the FSB is actually 208.9
Does anyone know why this happens.

Note: I'm new to overclocking so excuse my lack of know;edge

 

[fafner]

208.9 is almost 209. the clock is off by 0.1. is that something worth worrying about?

 

[CR0W M@GN3T]

no but i want to know why

and also its not just off by .1

when the motherboard is set to 222, the actual FSB is 221.1