In reply to davidbeynon:
Above the key you will find numbers for:
Longitude origin, scale, false easting, false northing, DX, DY,DZ, DA and DF.
Longitude, scale, fale easting and false northing go into the "user grid".
DX, DY, DZ, DA, DF go into "user map datum".
on my old garmin etrex I go to the grid and map datum menus and just keep scrolling until I find "user".
Post edited at 19:44