What does the setting knob on the altimeter adjust?

• A. Altitude and pressure
• B. Clockwise rotation only
• C. Temperature compensation
• D. Kollsman setting and position of the needles

Answer: (D)

The setting knob adjusts the reference pressure used by the altimeter—the Kollsman setting. By turning this knob, you change the pressure value shown in the Kollsman window (inHg or hPa). The altimeter uses that reference pressure to interpret the ambient air pressure, so as you change the setting, the instrument recalculates and the needle positions move accordingly to show the corresponding altitude. In practice, you set the local QNH (sea‑level pressure) to read altitude above mean sea level, or set standard pressure (29.92 inHg) to read pressure altitude. The knob itself isn’t about rotating in a single direction or physically modifying altitude; it provides the reference that changes the displayed altitude.