Follow the steps below on how to change Datum on the inReach SE & inReach Explorer.

1. Go to "Settings."

2. Select "Units."

3. Select "Datum."

4. Select a datum option (WGS84 is the recommended default).

More information on datums can be found here:

Basic definition: http://en.wikipedia.org/wiki/Geodetic_datum

Datum basics by ESRI: http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Projection_basics_the_GIS_professional_needs_to_know