Tektronix SPG8000 Technical Reference page 182

TIME button menu
170
Source. Use the left (◄) or right (►) arrow button to select from the following
timecode reference sources:
GPS Signal: This menu item appears only when Option GPS is installed. If
GPS Signal is selected, the time from the GPS receiver is used to derive the
time of day. This menu item is only available if GPS Signal is the selected
reference source in the REF button menu.
NOTE.
When you select GPS signal as the timecode reference source, then
depending on the GPS signal availability, it can take a while for the instrument to
lock to the GPS signal. During the time before the instrument locks to the GPS
signal, the instrument uses time based on the internal real time clock.
VITC Input: Selects the vertical interval time code as the timecode reference.
VITC is only available when the Reference Source is set to a video Genlock
signal.
NOTE.
When the VITC or LTC inputs are used as time-of-day sources, the
hh:mm:ss:ff settings will be synchronized to the VITC or LTC source (if present).
However, the yyyy-mm-dd settings will be set from the most recent valid source
(GPS or internal/manual).
LTC Input: Selects the LTC time code input as the timecode reference. This
menu item is only available when the function of the LTC connector is set
to Input.
Internal: Enables the Internal Time of Day mode. When the timecode
reference is set to Internal, an additional menu setting appears where you
can set the time manually (like setting any clock) and then activate the
time-of-day change.
CAUTION.
When Internal is selected as the timecode reference, the time-of-day
will not be automatically changed. (See page 3-132, How to set the time-of-day
in Internal mode.)
SPG8000 Technical Reference