NorthStar 957 Operator's Manual page 152

Chapter 11 - Setting up your 957
Choosing a
geodetic datum
Page 144
You may want to switch waypoints manually if you're
maneuvering around a waypoint in search of a lobster trap, or
trying to find a buoy in a thick fog. Manual switching lets you
keep a constant display of distance and bearing information
for the particular waypoint you're using until you tell the 957
otherwise. With manual switching, you manually change to
the next waypoint every time you arrive at the current
waypoint: Press the NAV LOG key, select the next leg or
waypoint if necessary, press the RESTART menu key, then
press the ENTER key.
Different parts of the world use various models for lat/lon
coordinates on their charts. Each model is called a datum. The
957's geodetic datum option contains all referenced datums,
according to Defense Mapping Agency publications.
You should always be sure that the datum the 957 uses
matches your Nav-Chart cartridge. All Navionics charts for the
last few years use WGS84, which is the 957's default. A few old
charts from areas such as South America have other datums.
Contact Navionics for more information. If you choose a
datum other than WGS84, an offset will be applied, but only to
the GPS lat/lon of your vessel's position. The vessel will be
moved on the chart, but not waypoints, routes, or track points.
To change the datum reference, on the NAVIGATION OPTIONS
screen, select the GEODETIC DATUM option and press the
EDIT menu key, then press the CURSOR PAD up and down to
scan through the alphabetic listing. When you see your
choice, press the ENTER key. For a list of the 957's available
datums, see Appendix C at the back of this manual.
You can specify a different datum for the 957's output ports than the one
set for the positional display. For instructions, see the Northstar 957
Installation Manual (part number GM957IM).
NOTE:
957 Operator's Manual, Rev. B