Garmin GPSMAP 182C User Manual

Page 77

GPSMAP 182/182C Owner’s Manual

AIN

ENU

NITS

• 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.

• Heading—selects the reference used in calculating heading

information. 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

you to specify the magnetic variation at your current location

and provides magnetic north heading references based upon

the variation you enter.

To enter a user deﬁned magnetic variation:

1. With the

Heading ﬁeld set to User Mag Var, highlight the

heading reference ﬁeld (immediately to the right), and press

ENTER.

2. Use the

ROCKER to enter the magnetic variation at your

current location, and press

ENTER.

WARNING: If User Mag Var is selected, you must periodically

update the magnetic variation as your location changes. Using

this setting, the unit does not automatically calculate and

update the magnetic variation at your present location. Failure

to update this setting can result in substantial differences

between the information displayed on your unit and external

references, such as a magnetic compass.