GEO Digital Earth Ground Resistance Tester - 

The Fluke 1623-2 earth ground tester is able to measure earth ground loop resistances using only clamps. With this test method, two clamps are placed around the earth ground rod and each are connected to the tester. No earth ground stakes are used at all. A known, fixed voltage is induced by one clamp and the current is measured using the second clamp. Then the tester automatically determines the resistance of the earth ground rod. This test method only works if a bonded earth ground system exists for the building or structure under test, but most are. If there is only one path to ground, like at many residential applications, the Stakeless method will not provide an acceptable value and the Fall-of-Potential test method must be used.