When an altimeter is changed from 30.11" Hg to 29.96" Hg, how does the indicated altitude change?

When the altimeter setting is changed from 30.11 inches of mercury (Hg) to 29.96 inches of mercury, the indicated altitude increases due to how altimeters function. Altimeters measure altitude by comparing the atmospheric pressure outside the aircraft to a standard pressure at sea level (29.92" Hg).

When the altimeter is set to a higher pressure of 30.11" Hg, it assumes that the aircraft is at a lower altitude because the higher the pressure setting, the lower the altitude indicated. Changing the setting to a lower pressure of 29.96" Hg indicates that the atmosphere is less dense, suggesting the aircraft is now at a higher altitude than what was previously indicated. Therefore, this change effectively makes the altitude reading go up, reflecting that the pilot is higher in the air than previously thought with the altimeter set to the higher pressure.

In practical terms, when the altimeter is calibrated to a lower pressure, the aircraft's true altitude increases relative to the pressure being measured. Thus, indicating a higher altitude than before when adjusting from a higher pressure setting to a lower one.