What does a watt-hour meter measure?

A watt-hour meter is designed to measure the total energy consumed by a device over time. It does this by recording the amount of electrical energy that flows through it in terms of watt-hours, which is a unit of energy equivalent to a watt of power used for one hour. This cumulative measurement helps users understand their energy usage, allowing for better management of consumption and costs associated with electricity.

The other options focus on concepts that are not related to the primary function of a watt-hour meter. For instance, while instantaneous power consumption pertains to how much power is being used at a specific moment, it does not provide insight into the overall energy consumed over time, which is essential for billing and efficiency assessments. Efficiency relates to how effectively a circuit converts electrical energy into useful work, but this is not something a watt-hour meter measures directly. Lastly, voltage levels pertain to the electrical potential in the circuit, which is not within the measurement scope of a watt-hour meter, as it focuses solely on energy consumption rather than voltage.