In an Airspeed Indicator (ASI), which type of pressure is measured in the case?

The Airspeed Indicator (ASI) is designed to measure the dynamic pressure of the airflow as it affects the aircraft. However, the case of the ASI itself is connected to a static port, which measures static pressure. This static pressure is crucial because it serves as a reference point against which the dynamic pressure is compared to determine airspeed.

When an aircraft moves through the air, it experiences dynamic pressure due to its velocity, which is measured using a ram air input. This ram air pressure is compared to the static pressure from the case of the ASI. Therefore, the case of the ASI specifically measures static pressure, which is vital for accurately calculating the difference needed to determine the indicated airspeed.

The options that refer to other pressure types, such as dynamic pressure, absolute pressure, and negative pressure, do not apply to the function performed by the ASI case. Dynamic pressure is what the ASI aims to quantify through the use of the static reference, while absolute pressure typically refers to total pressure measurements in a vacuum or a system where atmospheric pressure is not a factor, and negative pressure is not relevant in this context.