What happens to the altimeter when transitioning from high to low pressure?

When transitioning from high to low pressure, the altimeter will often overread. Altimeters are calibrated to a standard pressure setting (often 1013.25 hPa or 29.92 inHg), and they measure altitude based on this reference. When atmospheric pressure decreases, the actual altitude of the aircraft increases, but if the altimeter is not adjusted for the lower pressure, it will continue to indicate an altitude based on the higher pressure setting.

This phenomenon occurs because the machine assumes that the current atmospheric pressure is the same as the standard pressure setting. If the actual pressure is lower than anticipated, the altimeter's reading will display a higher altitude than what is truly being experienced. Pilots must remember to adjust their altimeters to ensure that they receive accurate altitude readings, especially during changes in weather conditions where pressure can shift significantly.

The alternative choices do not reflect this physiological principle of altimeters accurately:

• Underreading would indicate that the altimeter is indicating a lower altitude than what is actually present, which is not the case when transitioning to lower pressure.

• An accurate reading implies that the altitude displayed matches the true altitude, which cannot happen without adjustment.

• Shutting down is not a typical behavior for altimeters, as they are designed