The GDA 2020 thread prompted me to post about current rather than future conversions. (2020 compatiblity, according to keithy and Mark F in unison, is inconsequential. Good, one less thing to worry about.)
I searched recently for a the easiest way to make conversions from AGD66 to GDA94. I wanted to enter waypoints derived from old maps into a GPS device. I found a solution, then searched this forum in case anyone else had referred to AusDatumTool, the software I came across which offered that solution. Yes, AnthonyD, its creator had done so about five and a half years ago http://bushwalk.com/forum/viewtopic.php?f=5&t=2660&p=91819&hilit=ausdatumtool#p91819
AusDatumTool is still current, so it seems appropriate to start a new thread because that old thread was concerned primarily about the relation between WGS and Australian-based data. Not an issue that I want or need to know anything about. I should mention though that the software does include other datum sets: WGS84, NZGD49 and 2000, and ANG, which I see is from 1858 and measured in yards! As far as I know, there were no sets based on rods or chains.
There may be better software available for my simple task but I couldn’t find anything. In any case, this does everything I need. It’s a basic but I think well-designed tool. For example, when inputting the 6 or 7 digit Easting and Northing coordinates, an adjacent box labelled “Topo map” automatically shows how these references will be displayed in the traditional 2x3 digit form. Very useful if you are doing conversions while consulting old maps.
It can be demo-ed for free for a limited time, but it costs only $6. I almost passed it by when trawling the net because the top of the home page shows a Windows GUI and I use a Mac. But somehow managed to scroll down to see that running it on Mac or Linux can be easily done by installing a Windows emulator, with the relevant link to that being provided.
If anyone at my beginners level of learning about GPS usage is looking for an easy to comprehend solution to conversions, this should fit the bill. Perhaps experienced people might also find it handy if they are often needing a simple way to do conversions.