By Christopher Donahue, Updated Mar 24, 2022
The ohm meter is a cornerstone of electronic testing, measuring resistance by applying a small voltage and recording the resulting current. Whether housed in a classic D'Arsonval VOM with a needle display or a modern digital multimeter (DMM) with an LCD, mastering its use is essential for accurate measurements and circuit troubleshooting.
The ohm meter comes with two leads—typically red and black. Because resistance is measured on an unpowered circuit, the polarity of the leads is irrelevant. To test a discrete resistor, simply attach one lead to each end. If your meter uses probes, press them firmly onto the resistor terminals or wrap the resistor lead around the probe to ensure a solid mechanical connection.
Turn the meter on and set the range. Most VOMs have a front dial marked with the Greek letter Ω (omega). If you are unsure of the resistor’s value, start at the highest setting—usually the megohm range (M)—and step down until a readable value appears.
For analog VOMs, observe the needle. It should settle within the central 80 % of the scale. If it sits near an end, switch to a different range. Most needle displays have a reflective arc beneath the scale; view the meter straight on to eliminate glare. Align the needle with the correct scale (e.g., 1 Ω, 1 kΩ, 100 kΩ, 1 MΩ) to read the resistance.
With a DMM, the display shows the value in Ω, kΩ, or MΩ. If the measurement exceeds the current range, the display will flash or show OL (over‑limit). Simply select a higher range until the full value is displayed.
Repeat the process for each resistor. Analog displays take a bit of practice, but with a few trials you’ll read them confidently.
The ohm meter measures resistance by sending a small current through the test point. This must be done on an unpowered circuit. Measuring resistance while a circuit is live can give inaccurate results or, worse, damage the meter.
