Actually, Magnetic declination in Newcastle, Australia is*+12.41°*
Allan, at your sight near Coolah, well actually at the Black Stump near the turn off, it is:
Latitude: 31° 44' 44.5" S
Longitude: 149° 42' 21.2" E
Magnetic declination: +11° 19'*
Declination is*POSITIVE (EAST)
Inclination: 62° 28'*
Magnetic field strength: 56128.0 nT
So I would suggest using +11.2 degrees.
The source of this information is:
http://www.magnetic-declination.com/...le/122944.html
Just drag the map over to Coolah (Black Stump) and click on that spot on the map.
A box will appear with the above information enclosed.
I tried to pick out your driveway on the map and the website said +11.17 degrees if you want that level of precision.