If it is necessary to set the altimeter from 29.15 to 29.85, what change occurs?

• A. 700-foot increase in indicated altitude.
• B. 700-foot decrease.
• C. No change.
• D. 70-foot increase.

Answer: (A)

When you adjust the altimeter setting, you’re changing the reference pressure that the instrument uses to translate ambient pressure into altitude. Raising the setting from 29.15 to 29.85 increases the reference sea-level pressure. For the same actual atmospheric pressure at your location, this makes the altimeter read higher—the instrument thinks you’re higher above the reference surface. The change in reading is proportional to the change in setting: about 1 inch of mercury corresponds to roughly 1,000 feet near sea level, so a +0.70 inHg shift yields about a +700-foot increase in indicated altitude.