So, he built a single tool that combined multiple meter functions. If you're just looking to test an electrical receptacle, ...

The PeakTech P1073 is a €25 smart multimeter with functions like True RMS voltage, current, resistance, capacitance, ...

it has most of the functionality you would normally expect from a “multi”-multimeter – such as measuring both AC and DC voltage, current, capacitance and resistance – and on the other side ...