Altimeter

QNH

QNH is a sea-level pressure setting. With an appropriate local QNH, the Altimeter indicates altitude above mean sea level.

QFE

QFE is a station/reference-location pressure. It is useful when you want altitude relative to a particular reference level rather than mean sea level.

QNE

QNE uses the standard pressure setting of 1013.25 mbar / 29.92 inHg. In Marine Barometer it is an explicit fixed standard-pressure mode.

Altimeter reference source

The Altimeter can use either External Barometer Reference or Marine Barometer Reference. The reference source describes where the Altimeter gets its pressure setting. LINKED / UNLINKED may still appear as status information, but it is not the primary user choice.

Changing the Altimeter reference or setting changes the Altimeter indication. It should not change the normal Marine Barometer pressure reading.

When Barometer Lock starts

Starting the 60-minute Barometer Lock automatically initializes the Altimeter to QNH / External Barometer Reference using the Barometer's captured pressure. This makes the Altimeter immediately useful for a short excursion. After that initialization, the Barometer Lock is independent of later Altimeter changes.