Select > Preferences > Units.

System Units

Sets the unit format for the device. For example, Custom > Depth > Fathoms sets the unit format for depth to Fathoms.

Variance

Sets the magnetic declination, the angle between magnetic north and true north, for your present location.

North Reference

Sets the direction references used in calculating heading information. True sets geographic north as the north reference. Grid sets grid north as the north reference (000º). Magnetic sets the magnetic north as the north reference.

Position Format

Sets the position format in which a given location reading appears. Do not change this setting unless you are using a map or chart that specifies a different position format.

Map Datum

Sets the coordinate system on which the map is structured. Do not change this setting unless you are using a map or chart that specifies a different map datum.

Time

Sets the time format, time zone, and daylight saving time.