What happens to the altimeter indication if you change pressure setting during the flight?

• A. The altimeter will indicate a different altitude corresponding to the new reference pressure, altering the altitude reading
• B. It remains exactly the same
• C. It stops reading
• D. It shows vertical speed instead

Answer: (A)

An altimeter shows your altitude by converting ambient air pressure into a height using a reference pressure you set. The setting acts as the zero point for that conversion. So, when you dial in a different pressure, you’re changing where the instrument thinks “zero altitude” is, which shifts the height it displays for the same actual pressure you’re sensing.

If you increase the reference pressure, the same ambient pressure corresponds to a smaller altitude on the scale, so the readout drops. If you decrease the reference pressure, the readout rises. The aircraft’s actual height doesn’t change; only the display does.

That’s why pilots update the pressure setting to reflect local conditions (QNH) or the standard setting when required. It keeps the indicated altitude accurate relative to sea level or the flight plan, not because altitude physically changes, but because the reference point for the conversion changes.