Fluke 1621 earth ground tester fluke fluke 1621 the fluke 1621 is an easy to use earth ground tester for ground resistance testing the 1621 is the first line of defence in detecting reliable ground connections the unit features basic ground testing methods including 3 pole fall of potential as well as 2 pole ground resistance tests its convenient size rugged holster and large clear lcd display make it an ideal field earth ground tester for most electrical grounding work environments