Originally Posted by elmor
There is no such fluctuation, it's 100% a readout problem. Reference clock is not directly measured, but calculated using a suitable counter and prone to errors. The only platform which has hardware counters for reference clock is Skylake/Kaby Lake. Do you have any details on accuracy @Mumak
That's right - only very few CPUs allow true hardware measuring of BCLK (i.e. Skylake). For the rest we need to perform certain (often indirect) measurements to determine the BCLK and this can of course show slight fluctuations, especially under heavy system load.
HWiNFO has an option to disable BCLK "Periodic polling", so it will sample BCLK only once and don't perform periodic measurements and thus show fluctuations. I'm sorry, but there's no other way around this, as long as manufacturers don't offer a true measuring like in Skylake.