Following tables are useful for finding values DA, DF, DX, DY, DZ needed to setup User Datum
in your eTrex. (if you don't know, what "datum" is about ... take a look here). The user
datum consists from ellipsoid definition and reference point definition (shift):
Search Map-Datum-Index to find system used in your map. Enter values DX, DY, DZ (metric) into eTrex.
Find apropriate ellipsoid definition in Ellipsoid-Parameters-Index (from 2nd datum's column) and enter DA,DF.
Note, that all DX, DY, DZ, DA, DF values aren't absolute numbers, but are relative to WGS84 ellipsid (see
zero values at the WGS84 row).