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70 GPSMAP 198C Sounder Owner’s Manual
MAIN MENU > UNITS TAB
Units Tab
The Unit tab defines the Position Format, Map Datum, Heading,
Distance, Speed, Elevation, Depth, and Temperature units.
The following settings are available:
• Position Format—changes the coordinate system. You
should only change the position format if you are using a
map or chart that specifies a different position format or want
to use a format you are familiar with.
For additional information on Loran TD setup, see page
109.
NOTE: The Units tab settings affects how navigation
information appears on the GPSMAP 198C Sounder. When
in doubt, seek assistance. If you are using a map or chart in
conjunction with your GPS, make sure the settings under the
Units tab of the GPSMAP 198C Sounder match that of the
map or chart. This information should appear somewhere on
the map or chart. If the information is not present, contact the
map or chart maker to determine what position format, datum,
heading and units of measure are being used for the map or
chart.
• Map Datum—sets the datum reference used to determine
a given location. The default setting is WGS 84. The
unit automatically chooses the best datum depending on
your chosen position format. Datums are used to describe
geographic locations for surveying, mapping, and navigation.
You should only change the datum if you are using a map or
chart that specifies a different datum.
WARNING: Selecting the wrong map datum can result in
substantial position errors. Unless otherwise specified by
the navigation documentation you are using, use the default
WGS 84 datum for best overall performance.