How does atmospheric pressure affect altimeter readings?

Atmospheric pressure has a direct relationship with altimeter readings, primarily because altimeters are calibrated to measure changes in pressure to determine altitude. When atmospheric pressure changes, the altimeter can provide readings that deviate from true altitude.

As altitude increases, atmospheric pressure decreases. If the pressure at the surface is lower than what the altimeter is set to, the altimeter will indicate a higher altitude than actually exists. Conversely, during higher pressure conditions, the altimeter may indicate a lower altitude than one is truly at. Therefore, fluctuating atmospheric pressure – due to weather systems or changes in density altitude – can significantly impact the accuracy of the altimeter, leading to erroneous altitude readings.

Understanding this principle is essential for pilots when flying in varied weather conditions, as incorrect altimeter settings can lead to dangerous misunderstandings of one's true altitude and, consequently, affect navigation and safety during flight.