This GFCI tester uses advanced circuitry and a patent-pending proprietary design to precisely detect the required low resistance (less than 10ohms) on ground wire and provides a clear and easy-to understand single LED readout indication for correct wiring or Bad Ground, Open Neutral, Hot/GND Reverse, Hot/NEU Reverse and Open Hot wiring errors without the need to memorize or decipher a dual-indication chart.