Which of the following best defines the purpose of a manometer?

The purpose of a manometer is to measure pressure difference, making the choice regarding pressure difference the correct one. Manometers are instruments designed to measure the pressure exerted by a fluid at a given point in comparison to another point, typically atmospheric pressure. This capability is crucial in various applications, including HVAC systems and research environments, where pressure differences can indicate airflow characteristics or potential leaks in a building’s envelope.

Pressure measurement is vital for ensuring that systems operate efficiently and within the required specifications. By identifying pressure differences, technicians can assess whether a building is adequately airtight or if adjustments are needed for optimal performance. Thus, the focus on pressure difference aligns directly with the aims of whole-building airtightness testing, where maintaining specific pressure conditions is essential for energy conservation and establishing a healthy indoor environment.

The other options, while related to measurements, do not pertain to the specific function of a manometer. Measuring liquid levels and airflow rates require different types of instruments, and temperature measurement is also outside the scope of what a manometer is designed to do.