G-Shock GW-9200BPJ-1 - Manual (Page 51)

E-49
Other Altimeter Mode Features
This section explains other features and settings that are available in the
Altimeter Mode. Note that all of the information in this section applies to all
types of Altimeter Mode measurements, unless specifically indicated
otherwise.
Specifying a Reference Altitude
After you specify a reference altitude, the watch adjusts its air-pressure-to-
altitude conversion calculation accordingly. The altitude readings produced by
this watch are subject to error caused by changes in air pressure. Because of
this, we recommend that you update the reference altitude whenever one is
available during your climb.