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How to test resistors
Remove power from the circuit containing the resistor.
This can be done by unplugging it from the mains or by removing the batteries if it is a portable device. Keep in mind that some devices still can be charged with a potentially harmful voltage until minutes after removing its power!
Isolate the resistor from the circuit.
An attempt to measure a resistor that is still connected to the circuit can yield an incorrect calculation, as part of the circuit might also be measured. Disconnect one end of the resistor from the circuit.