Garmin G3X Touch Pilot's Manual page 66

Flight Instruments
GLIDESLOPE - ILS SOURCE
The Vertical Deviation (Glideslope) Indicator (VDI) appears to the left of the altimeter
whenever an ILS frequency is tuned in the active NAV field of an external navigator.
A green diamond acts as the VDI Indicator, like a glideslope needle on a conventional
indicator. If a localizer frequency is tuned and there is no glideslope signal, "NO GS"
is annunciated.
48
Vertical
Deviation
Source
Vertical
Deviation
Indicator
Vertical Deviation Indicator
(Glideslope-ILS Source)
Garmin G3X Touch Pilot's Guide 190-01754-00 Rev. E