When using a negative offset, for example -100mV for Cores HWInfo32 shows 1.945V. I suspect you are treating the offset as an unsigned number instead of signed.
Thanks for the report. Please copy-paste the exact line where it shows this invalid value and tell me the exact setting in BIOS for this case. I'll fix it then.
I think there's still a small problem with both positive and negative numbers in that each bit should be 1/1024th of a Volt, not 1mV (1/1000). The two screenshots should be -80mV I believe. Also reads -82mV in build 2075. It's only going to make a small difference so not a big thing.
Well if it's not then XTU is wrong. Offset is given in steps of 0.9765625mV which is 1/1024V. Remember I didn't say I was sure, I said "I think". Unfortunately that's the best I can offer you.