Setup/Units/Position Format > select MGRS
Setup/Units/Map Datum > select WGS84
This will give you an easy read for all the current NSW Topo maps which have an orthophoto (and bad paper). All you are really concerned with will be the first three numbers of the eastings and northings, though your Etrex will also display Grid Zone and hundred thousand metre identifier. While current maps are on GDA94 (look for 'Control' in the map legend) unless you are a surveyor they are the equal to the World Geodetic System.
For the older topo maps without the photo (and on less bad paper) based on the old datum AGD66, the third number on the easting and northing will be different by 1 and 2. So you either reset Datum to AGD66 or just buy a current map. You sometimes hear of people being astray by a couple of hundred meters and going up the wrong garden path.
If you have to relay location info for any reason, the first thing you give is the map name, then the Location Data (see instructions in the 'Grid References' box in the map legend).
Its also hand to set up your Etrex display so that Location is in the top box, so that when you 'Page' through the various dispalys your 'Location' is easy to find when you arent thinking too straight. The guys at Garmin seem pretty understanding about allaying niggling uncertainties, worth buying your local map and learing your way round the little yellow box first.
Hope that helps
Rgds.
Its all in the legend
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