Basics

A plug-in power meter can help reveal appliance energy use, but a large display does not guarantee useful measurements at every load.

The ground clip on a conventional bench oscilloscope probe is usually connected to protective earth through the instrument.

Two meters can disagree on the same AC circuit because they interpret the waveform differently.

A continuity beep confirms that the meter detected a conductive path under its test conditions.

Clamping around an entire appliance cord can produce a near-zero current reading while the appliance is running.

An auto-ranging meter can change its decimal point and unit prefix while the measured quantity barely changes.

More display digits can reveal smaller changes without making a multimeter more accurate.

A non-contact voltage pen is a useful warning tool, but a silent pen does not prove a circuit is safe to touch.

A voltmeter looks across two points; a direct-reading ammeter becomes part of the current path.

A shiny metal part can look surprisingly hot or cold in a thermal image without having that surface temperature.