How is resistance measured?

Resistance is measured using an ohmmeter. An ohmmeter is specifically designed to measure the resistance of electrical components by applying a known voltage and measuring the current that flows through the component to calculate its resistance using Ohm's Law (R = V/I). This instrument is essential for diagnosing electrical issues, testing components, and ensuring that circuits function correctly.

The other options pertain to different electrical measurements: a voltage meter measures voltage, an ammeter measures current, and a wattmeter measures power in watts. Each of these instruments serves a distinct purpose in electrical measurements, but none are designed to measure resistance directly, making the ohmmeter the correct choice for this question.