Customer brought in a project last week — claims his 5V regulator is "fluctuating". Showed me his multimeter reading 4.9V → 5.2V → 4.7V randomly. Naka-charged yung battery ng meter, decent unit (Fluke 17B+).
Nag-probe ako with my own scope side by side. Scope: rock-stable 5.00V flat trace. So bakit jumpy yung multimeter?
Turned out: not the supply. The multimeter was picking up RFI from a nearby WiFi router on his bench. Moved meter ~1 meter away from the router, reading became rock-stable 5.0V on his Fluke too.
Sharing kasi when readings look noisy, always question yung meter before yung supply. Especially with cheap meters and high-frequency sources around. Yung mga PHP 500 multimeters as expected, but even the better ones can pick up RF if antennas are close.