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What kind of short are u talking about?
Why would it be in the millivolts?
Do you mean, measuring from VCC to ground on each IC chip and what component is connect to the VCC and ground rails?
So how do u know where the short is? there is NO voltage drop from VCC to ground on that component?
The techniques relies on there being some voltage drop along the power lines. It will be very small, which I why you need to measure millivolts or fractions of millivolts.
It is not measuring the voltage across the component or short circuit.