The PZEM-051 has a non-volatile memory (saves data after power loss). It typically comes with two buttons on the front or side: and Set (or similar, depending on revision).
The Peacefair PZEM-051 is the silent accountant of your DC electrical system. It transforms guesswork into data, allowing you to optimize battery usage, detect failing equipment (sudden increased current), and truly understand your energy habits. peacefair pzem-051 manual