Thanks for the timely reply!
Yes, I can comfirm that by listening to the fan and watching the numbers in HWiNFO. And TACH(0) seems to provide the RPM number with more precision.
Also maybe due to some bug in my model's EC/ACPI imp'l, _TZ_.RFAN(0) tend to jump erratically, ranging from 100 to several tens of thousands, so I would like to know is there a way to customize AIDA64's reading a bit.
Thanks!