Australia's main datum for mapping and locating points on the australian continent is changing. You can occasionally find old maps using AGD66 in some shops, these are out of date. In 2000 GDA94 was adopted and now it too is changing. GDA2020 is here! Have no idea what I'm talking about?
Here is a good video that explains the change:
https://vimeo.com/191566518
While I'm on spatial data... why not increase the accuracy of your GPS? Many new GPS units have a WAAS option. Enable this and you will have greater accuracy in all three spatial dimensions. Of course it only works when certain satellites are visible to your GPS, in northern Australia it will detect the Indian and Japanese satellite systems but in Victoria and Tasmania you may find it harder to find a satellite that has WAAS type capabilities.
Want to know more about WAAS:
https://www.youtube.com/watch?v=CeIEs9l9aws
