Eagle 642c df igps User Manual

76

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 map cursor,
you can scroll over 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 set range rings: From the Map Data menu, highlight 

and press 

 to turn them on (check) or turn them off (uncheck). After

the option is set, press 

.

To set Lat/Long Grid: From the Map Data menu, highlight 

 and press 

 to turn them on (check) or turn them off (un-

check). After the option is set, press 

 repeatedly to get back to the

main page display.

Map Datum Selection

Maps and charts are based on a survey of an area covered by a map or
chart. These surveys are called Datums. Maps created using different
datums will show the same latitude/longitude in slightly different loca-
tions.

All datums have a name. The GPS system is based on the WGS-84 da-
tum, which covers the entire world. Other datums may cover the entire
world or just a small portion of it. By default, your position is shown
with the WGS-84 datum. It, however, can show your position using any
of 191 different datums.

To change the Datum:

1. Press 

|

|

↓ to 

|

|

↓ to 

|

.

2. Select the desired datum and press 

.

3. To return to the main page display, press 

|

.

A list of the datums used by this unit is in the back of this manual.