They're doing a variation on the second method I mentioned.
Instead of shunt resistances in series with the inductors of the Vcore regulators, they have loops of wire going through a clamp on current probe.
Accuracy most likely sucks, because of the high frequency 'noise' I mentioned earlier. Clamp on ammeters generally have lousy accuracy anyway. High frequency signals, on top of the DC component that the ammeter is attempting to measure, is not going to help the accuracy any.
Still, it is a way to get some kind of number...
Another issue, is that not all of the power dissipation is going to occur in the CPU itself. Some fraction is going to be dissipated in the Northbridge. This is a wild ass guess, but I wouldn't be surprised if 5% of the Vcore regulator's output power, is dissipated in the Northbridge during very memory intensive operations.
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