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CPU-z and keep it open. There should be a box called VCore. There, it should say what the current voltage is. Write this number down. Then run Prime95/Orthos and and continue to watch that VCore box. Run the test for 10min and write the lowest number you see there. Subtract the second number from the first. That is your VDroop. A bad VDroop would be anything greater than .1V. For example, I have a horrible VDroop because mine is .13V.