Measuring resistance on a component in a circuit will cause inaccurate readings because the multimeter is also measuring resistance from the other components in a circuit as well as the one being tested. Sometimes, however, it is necessary to test resistance on components in circuit.
 Current flowing through a circuit will cause inaccurate readings, as the increased current will create a higher resistance. Also, the additional voltage could damage the multimeter. (For this reason, testing the resistance of a battery is not advised.)


Any capacitors in a circuit being tested for resistance should be discharged before testing. Discharged capacitors may absorb charge from the multimeter's current, creating momentary fluctuations in the reading.
 Diodes conduct electricity in only 1 direction; thus, reversing the position of the multimeter's probes in a circuit with diodes will cause different readings.
 Some resistors or components need to be held in place to maintain contact with the multimeter's probes. Touching the resistor or the probe with your fingers can cause inaccurate readings due to your body absorbing current from the circuit. This is not a significant problem when using a low-voltage multimeter, but it can be a problem when testing resistance with a high-voltage multimeter.


One way to keep your hands off components is to attach them to a testing board, or "breadboard" when testing for resistance. You can also attach alligator clips to the multimeter probes to keep the terminals of the resistor or component in place while testing.
Test resistance on components not in a circuit.
Test only components that are powered off.
Check for diodes in the circuit.
Watch your fingers.
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