The Ultimate questions on Linux, the Universe, and Everything

I bought a cheap AC panel meter from AliExpress: voltage, current, power, frequency, power factor and energy in one module, 20 A direct through an internal shunt. Because it runs from a separate 8–18 V DC supply and measures from 0 V up to 500 V AC, it suits a variac in a lab. Some listings even call it a variac meter. When it arrived there was no manual in the box. The listing had a few photos and a table of settings, and a search turned up nothing from a manufacturer. That’s normal for this kind of part, and it’s a problem if you want to put one in a real project. How much does it dissipate? Is the supply isolated? What can the alarm output handle?   The settings are also printed on the rear panel, but they are hard to decipher, and the listing’s table gives more information. I haven’t seen this table in other places where the meter is listed, such as Amazon. And when you search online or ask AI, you get partly wrong information.     The only other documentation I ...