Which of the following precautions should be taken when measuring in-circuit resistance with an ohmmeter?

An ohmmeter determines resistance by applying a small, known voltage from its internal battery to the component being tested and measuring the resulting current flow. If the circuit is powered on during this test, the circuit's own voltage will interfere with the ohmmeter's measurement. This will not only result in wildly inaccurate readings but can easily overload and permanently damage the meter's internal circuitry. Always ensure the equipment is unplugged or powered down, and that any large capacitors are safely discharged, before attempting to measure resistance.