Furuno GP-3500F Operator's Manual page 131

SELECT NAV SOURCE
Selects the source of position data from among INT (internal), EXT (external),
EXT (external) LORAN-C and ALL. For details, see the installation manual.
When selecting EXT, EXT LORAN-C or ALL, "EXT" appears at the bottom of the
PLOTTER (PILOT) display.
LOCAL TIME (INT GPS)
GPS uses UTC time. If you would rather use local time, key in the time
difference between it and UTC time. Use the [CURSOR ON/OFF] key to switch
from "+" to "-" and vice versa. The setting range is -13:30 to +13.30.
LOCAL TIME (EXT NAV)
If the NMEA time data fed from external equipment is wrong and cannot be
corrected at the external equipment, enter an offset here to correct it. Use the
[CURSOR ON/OFF] key to switch from "+" to "-" and vice versa.
GEODETIC DATUM
Your unit is preprogrammed with most of the major chart systems of the world.
Although the WGS-84 system, the GPS standard, is now widely used other
categories of charts still exist. Select the chart system used, not the area where
your boat is sailing.
1. Rotate the [ENTER] knob to select GEODETIC DATUM.
2. Roll the trackball in left-right direction to select the chart system you are
using.
The geodetic datum system selected appears at the bottom of the PLOTTER (or
PILOT) display.
WGS84: WGS-84 is selected.
TOKYO: TOKYO-MN is selected.
LOCAL: Other chart system is selected.
POSITION SMOOTHING
When the DOP or receiving condition is unfavorable, the GPS fix may change,
even if the vessel is dead in water. This change can be reduced by smoothing
the raw GPS fixes. A setting between 000 to 999 is available. The higher the
setting, the more smoothed the raw data, however too high a setting slows
response time to change in latitude and longitude. This is especially noticeable
at high ship's speeds. 000 is the normal setting; increase the setting if the GPS
fix changes.
9. CUSTOMIZING YOUR UNIT
9-17