| Problem | Likely Cause | Fix | | :--- | :--- | :--- | | Fluctuating readings | Poor probe contact | Press firmly, scrape corrosion | | Negative resistance | Probes reversed polarity | Swap red/black sets | | Reading 0.00 mΩ | Dead battery in tester | Replace 8x AA | | OL (overload) | Resistance too high | Change to Ω range (press RANGE) | | Noise symbol (~) | Nearby inverter/motor | Shut off large loads or use clamp-on noise filter (Hioki 9269) |