To be exact, each GDDR chip has 4 relatively easily accessible measuring points on the backside, each chip has 4 surface mount capacitors that are bigger than the rest. The other pole is always vMEM, the other is ground. So the label "more accurate vMEM reading" applies to all of these 4 capacitor per GDDR chip and all GDDR chips - not just the one cap it points to in the pic.