What device is primarily used to measure humidity?

The device primarily used to measure humidity is a hygrometer. A hygrometer measures the amount of moisture in the air, which is essential for understanding humidity levels.

While a psychrometer can also measure humidity, it does so indirectly by using the difference between the temperatures of two thermometers, one dry and one wet. This means a psychrometer requires additional calculations and is typically used in more specific scientific or meteorological contexts.

In contrast, a thermometer is designed to measure temperature and does not relate directly to humidity measurement. A pulse oximeter is used to measure the oxygen saturation level in the blood, which is unrelated to humidity measurement.

Understanding the primary purpose of each device clarifies why a hygrometer is the most direct answer for measuring humidity.