Firmware is somewhat buggy: When voltage increases over 178.1V, volts display just freezes on last displayed volts value, no overload condition is displayed. So, volts display will be false above 178V. Same for current: above 9.99A, no overload is displayed. Even worse: if voltage increases quickly (faster than display refresh rate), for example from 150V to 180V, 150V will be displayed forever. Same behaviour with current. Otherwise, a fine wattmeter at a reasonable price. It's a pity it has such a beginner's bug.