Rotating the altimeter's setting knob to a higher (or lower) barometric setting moves the hands to higher (or lower) indicated altitude at the rate of 1 inch Hg to 1,000 feet of altitude. Given the current altimeter setting of 30.42 and the indicated altitude of 6,500 ft., resetting the window to 29.92 would lower indicated altitude by how many feet?

Rotating the altimeter's setting knob to a higher (or lower) barometric setting moves the hands to higher (or lower) indicated altitude at the rate of 1 inch Hg to 1,000 feet of altitude. Given the current altimeter setting of 30.42 and the indicated altitude of 6,500 ft., resetting the window to 29.92 would lower indicated altitude by how many feet?

• A. Increase by 500 ft
• B. Decrease by 1000 ft
• C. Decrease by 500 ft
• D. Increase by 1000 ft

Answer: (C)

Main idea: The altimeter setting aligns the instrument’s reference sea-level pressure with the actual pressure. Changes in the setting shift the indicated altitude by about 1000 feet per 1 inch of mercury, with the direction of the shift depending on whether you move the setting up or down. Here, the setting is lowered from 30.42 to 29.92, a decrease of 0.50 inHg. A lower setting makes the altimeter indicate a lower altitude for the same ambient pressure, so the indicated altitude decreases by 0.50 × 1000 ft = 500 ft. Starting at 6,500 ft, the new indicated altitude would be 6,000 ft, a drop of 500 ft.

Main idea: The altimeter setting aligns the instrument’s reference sea-level pressure with the actual pressure. Changes in the setting shift the indicated altitude by about 1000 feet per 1 inch of mercury, with the direction of the shift depending on whether you move the setting up or down.

Here, the setting is lowered from 30.42 to 29.92, a decrease of 0.50 inHg. A lower setting makes the altimeter indicate a lower altitude for the same ambient pressure, so the indicated altitude decreases by 0.50 × 1000 ft = 500 ft. Starting at 6,500 ft, the new indicated altitude would be 6,000 ft, a drop of 500 ft.