Data storage function. Easily record the voltage at different times or in different environments, up to 20 groups can be stored. The socket status is shown by the LED display, and the 7 statuses are easy to judge : OK, L/N REVERSE, N OPEN, L/N REVESRE, E OPEN, N/E REVERSE, L/E REVERSE AND E OPEN. Advanced socket tester, used to quickly detect if the outlet wiring is correct. Small size, portable design, one-touch operation, easy to use, plug and play. Electrical tester tests GFCI device by simulating ground fault conditions. It operates on the GFI outlet and confirms operation of the ground fault protection device. It is very suitable for protecting your safety from fear of electric shock. Be careful when using this feature on regular outlets. It can trip house wiring. It is widely used in electrical maintenance testing, desktop outlet testing, power supply board testing, and wall outlet testing in social areas such as homes, schools, offices, factories, etc. The home improvement acceptance and safety inspection will save you a lot of time in detecting socket problems.