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Location Sub Tab
Use the Location sub tab to change location setting information.
To access the Location sub tab:
1. Highlight the Setup tab on the Main Menu.
2. Select the Location sub tab.
See the “Appendix” for more information about location formats
and map datums. Also visit the National Imagery and Mapping
Agency at www.nima.mil for more information on grids and datums.
Changing the Location Format
When you change the Location Format, you change the coordinate
system in which a given location reading appears. The default
format is latitude and longitude in degrees, minutes, and thousandths
of a minute (hddd°mm.mmm). Only change the location format if
you are using a map or chart that species a different location format
or want to use a format you are familiar with.
Selecting a Different Map Datum
Datums are used to describe geographic positions for surveying,
mapping, and navigation and are not actual maps built in the unit.
Only change the datum if you are using a map or chart that species
a different datum.
The default setting is WGS 84. The unit automatically selects the
best datum depending on your chosen location format.
WARNING: Selecting the wrong map datum can result in
substantial position errors. When in doubt, use the default
WGS 84 datum for best overall performance.
Selecting a Different Heading Reference
You can select from Auto Mag Var, True, Grid, and User Mag Var.
Auto Mag Var provides magnetic north heading references that are
automatically determined from your current location. True provides
headings based on a true north reference. Grid provides headings
based on a grid north reference (and is used in conjunction with
the grid position formats). User Mag Var allows you to specify the
magnetic variation at your current location and provides magnetic
north heading references based on the variation you enter. Enter
the magnetic variation of your current location in the Magnetic
Variation eld if you selected User Mag Var for the heading.
WARNING: If User Mag Var is selected, the unit does not
automatically calculate and update the magnetic variation at
your present location. You must update the magnetic variation as
your location changes. Failure to update this setting can result in
substantial differences between the information shown on your
unit and external references, such as a magnetic compass.
90 GPSMAP 378/478 Owner’s Manual
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