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Map Overlays (Range Rings; Lat/Long Grid)
The map screen can be customized with four range rings and/or grids
that divide the plotter into equal segments of latitude and longitude.
Range rings are handy for visually estimating distances on the map. The
ring diameters are based on the current zoom range. For example: at the
100 mile zoom, the screen will show two rings with your current position
in the center. The large ring touching the left and right sides of the
screen is 100 miles in diameter (same as the zoom range). The second
smaller ring is 50 miles in diameter (always 1/2 the zoom range).
The distance from your current position to the smaller ring (the ring's
radius) is 25 miles (always 1/4 the zoom range). With the arrow keys
and map cursor, you can scroll the map to see the third and fourth
rings. In this example, the distance to the third ring is 75 miles and
distance to the fourth ring is 100 miles from your current position.
To turn on/off range rings:
1. From the Map Page, press
MENU|↓ to MAP DATA|ENT.
2. Press ↓, → to
RANGE RINGS. With the option highlighted, press ENT to
check it (turn on) and uncheck it (turn off.)
3. After the option is set, press
EXIT|EXIT to return to the page display.
To turn on/off Lat/Long Grid lines:
1. From the Map Page, press
MENU|↓ to MAP DATA|ENT.
2. Press ↓, to
LAT/LON GRID LINES. With the option highlighted, press ENT
to check it (turn on) and uncheck it (turn off.)
3. After the option is set, press
EXIT|EXIT to return to the page display.
Map Datum Selection
Maps and charts are based on a survey of an area covered by the map
or chart. These surveys are called Datums. Maps using different da-
tums will show the same latitude/longitude in different locations.
All datums are named. The GPS system is based on the WGS-84 da-
tum, which covers the entire world. Other datums may also cover the
entire world, or just a small portion of it. By default, your unit uses the
WGS-84 datum. It, however, can show your position using any of 191
datums. Different datums can be selected. To change the datum:
1. Press
MENU|MENU|↓ to GPS SETUP|ENT|↓ to DATUM SELECTION|ENT.
2. Use ↓ ↑ to select the desired datum, then press
ENT.
3. To return to the last page displayed, press
EXIT|EXIT.
A list of the datums used by this unit is in the back of this manual.