A resistance meter, or ohmmeter, is a testing instrument that measures electrical resistance. Most ohmmeters are digital devices, although analog variants are available to measure rapidly fluctuating values.
Ohmmeters work by passing a constant current through the resistance, with a second circuit that measures voltage across that resistance. A microcontroller or microprocessor then uses Ohm's Law to divide the voltage by the current and display the resulting resistance value to the user.
Resistance meters are suitable for a huge variety of applications, from circuit testing on boards or small electronic devices, to insulation testing on motors, transformers or other heavy machinery.