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The instrument used to measure the wattage consumed by an electric motor is the wattmeter. A wattmeter is designed to measure the actual power (in watts) that is being used in an electrical circuit, which accounts for both voltage and current.

This is particularly crucial when assessing the performance of electric motors, as you're interested in the true power they are consuming to understand efficiency, potential issues, or performance in relation to their specifications. The wattmeter incorporates measurements of both voltage (in volts) and current (in amperes) and computes the product of both, adjusted for the phase difference with AC systems.

This is distinct from devices like a voltmeter, which measures voltage only; an amp meter, which focuses on current; and an ohmmeter, which measures resistance. Each of these instruments serves a specific purpose in electrical diagnostics but does not measure power directly, which is why they are not suitable for assessing wattage consumption by electric motors.