CPU speed detection not always same

[testlog]

i run several times burnin test at same platform.
but the CPU speed detection is not always same.
sometimes is 499.9MHz, sometimes 499.5,sometimes 500.2
why?
my CPU setting under bios is 500MHz.

[David (PassMark)]

We measure the speed of the CPU. Not just display the value claimed by BIOS. The measurement process isn't exactly precise nor is the clock in your system. So small variations are possible. However the 0.14% variation you are seeing is pretty good I think.

[testlog]

ok.
just worry if this is motherboard issue.