Which instrument depends on static pressure to indicate height above sea level?

The altimeter is the instrument that relies on static pressure to indicate height above sea level. It operates based on the principle that atmospheric pressure decreases with an increase in altitude. As an aircraft ascends, the static air pressure around it decreases, and the altimeter uses this decrease to determine the aircraft's altitude.

An altimeter typically measures this pressure in inches of mercury (inHg) or millibars (mb), which provides the pilot with a calibrated readout that represents altitude above sea level. It is essential for maintaining proper flight levels and ensuring safe altitude separation from terrain and other aircraft.

The vertical speed indicator measures the rate of climb or descent, but it does so based on the rate of change of static pressure rather than providing a direct altitude reading. The airspeed indicator measures the dynamic pressure created by the motion of the aircraft through the air, and the heading indicator is used for navigation to show the direction the aircraft is facing. Hence, only the altimeter provides altitude information directly tied to variations in static pressure.