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If the pilot increases the reference pressure using the sub-scale setting knob, the altitude indicated by the altimeter:
  • A
    decreases if QNH < 1013 hPa.
  • B
    decreases if QNH > 1013 hPa.
  • C
    decreases.
  • D
    increases.

Check the attached diagram. When the pilot increases the reference pressure setting, it means that the pressure datum is physically lower than the previous one (atmospheric pressure increases when height decreases). For example, 1020 > 1015. Therefore, the higher the pressure setting, the bigger the distance between the aircraft and the pressure datum.

As you can see from the diagram, the distance Y is bigger than X because we increased the pressure setting from 1015 hPa to 1020 hPa.

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