What condition will likely cause an altimeter to read incorrectly?

An altimeter relies on atmospheric pressure to determine altitude. When flying, the air pressure around the aircraft changes due to various factors, including weather conditions and altitude. If the altimeter is not adjusted to reflect the current atmospheric pressure, it can provide an inaccurate reading.

For instance, the altimeter is typically set to a standard pressure setting (29.92 inHg) at sea level, but actual seasonal pressure variations or rapidly changing weather conditions may not match this standard. If the pilot fails to adjust the altimeter for local barometric pressure, the readings may be significantly off, which can result in flying lower or higher than intended.

The other conditions presented do not directly relate to the accuracy of the altimeter readings. Flying at a constant altitude, using updated calibration methods, or operating in controlled airspace do not inherently cause erroneous altitude readings as long as the altimeter is properly set to the current atmospheric pressure.