An ohmmeter is an electronic device that measures electrical resistance, such as that of a circuit component. Ohmmeters come with different levels of sensitivity, some are designed to measure low-resistance materials, while others measure higher resistance.
An ohmmeter functions by passing a constant current or voltage though an object, such as voltage from a battery, and then measuring the resulting voltage with an ammeter after it passes through the resistance. The higher resistance the material has, the less current will pass through it. An ohmmeter is typically not used to measure resistance across an entire circuit, but rather through different parts of the circuit, although it can be used to test that a circuit is not broken. Components of a circuit can be removed and tested individually for resistance.