Datum; Pcf - Eagle Explorer Installation And Operation Instructions Manual

them, if needed. Once this is done, an internal clock will keep the correct
time, even when the unit is turned off. The GPS system updates this
clock when the unit is locked on to the satellites.

DATUM

Maps and charts are based on a survey of the area that's covered by the
map or chart. These surveys are called "Datums". Maps that are created
using different datums will show the same latitude/longitude in slightly
different locations.
All datums are named. The GPS system is based
on the WGS-84 datum, which covers the entire
world. Other datums may also cover the entire
world, or just a small portion. By default, the Eagle
Explorer shows your position on the map using
the WGS-84 datum. However, it can show your
position using one of 189 different datums.
To change the datum, first press the MENU key,
then highlight the "GPS Setup" label and press
the right arrow key. Now highlight the "Select Da-
tum" label. Finally, press the right arrow key again.
A screen similar to the one at right appears.
The WGS-84 label is highlighted. To change it, simply press the up or
down arrow keys to highlight the desired datum, then press the ENT key.
This selects the datum and erases the select datum menu.
PCF (Position Correction Factor)
Another method used to make your display match a chart or map is
called "PCF" or Position Correction Factor. This unit gives you the capa-
bility to move or offset the position shown on the display to match one on
the chart. The unit will add this offset to all position and navigation dis-
plays at all times.
Remember, the position error on any radio navigation system is very
dynamic and the PCF offset should never be used in an attempt to can-
cel the error.
In general terms, PCF should only be used if your map indicates what
the possible error is. PCF should always be reset to zero when you're
finished with the chart.
For example, suppose you are stopped at a location that is accurately
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