How does the altimeter operate to measure altitude?

The altimeter operates by detecting changes in barometric pressure and using that information to determine altitude. It is primarily based on the principle that atmospheric pressure decreases with an increase in altitude. The device contains an aneroid wafer, which is a sealed metal chamber that expands and contracts with changes in pressure. As altitude increases and the air pressure decreases, the aneroid wafer will expand, and the altimeter mechanism translates this movement into a visual altitude reading.

This functionality is crucial for pilots, as it allows them to maintain a safe and accurate altitude during flight. The altimeter is calibrated to measure pressure in inches of mercury (inHg) or millibars, translating these values into feet or meters pertaining to sea level, depending on the setting.

The other answer choices do not accurately explain how a traditional altimeter works, which reinforces why the correct answer focuses on the barometric pressure detection mechanism. For instance, the reliance on temperature affects air density but is not the primary function of the altimeter itself. Similarly, ground speed and distance calculations pertain to other instruments, like the groundspeed indicator and GPS systems, rather than measuring altitude directly.