Eagle Electronics 642c iGPS manual Map Datum Selection

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 RANGE RINGS and press ENT to turn them on (check) or turn them off (uncheck). After the option is set, press EXIT.

To set Lat/Long Grid: From the Map Data menu, highlight LAT/LON GRID LINES and press ENT to turn them on (check) or turn them off (un- check). After the option is set, press EXIT 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 MENUMENU↓ to GPS SETUPENT↓ to DATUM SELECTIONENT.

2.Select the desired datum and press ENT.

3.To return to the main page display, press EXITEXIT.

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

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