Which device could be used in conjunction with a static tap to measure pressure differences in a duct?

The manometer is the correct choice for measuring pressure differences in a duct. This device is specifically designed to measure the pressure of gases and liquids and can easily indicate the difference in pressure across two points within a system, such as a duct. By using a manometer alongside a static tap, which measures static pressure at a certain point, technicians can determine how pressure varies throughout the ductwork. This information is essential for assessing system performance, airflow rates, and overall efficiency.

In contrast, a barometer measures atmospheric pressure but is not suited for gauge pressure differences within confined structures like ducts. A hygrometer is used to measure humidity levels in the air, which does not relate directly to pressure measurement. Similarly, a flow meter quantifies the volume or mass flow rate of a fluid but does not measure pressure directly. Therefore, while these other devices serve valuable purposes, they do not provide the necessary functionality required for measuring pressure differences in conjunction with a static tap in duct systems.