Swiss NAV-D Manual page 11

BI-DIRECTIONAL 12-HOUR GMT BEZEL
The NAV-D comes with a 12 hour GMT bezel which allows for easy tracking of time
in two different time zones.
Rotate your bezel to align the 12 o'clock bezel marker to local time-zone offset.
Read the watch as normal for home time, and off the bezel for local time.