[Outbackmanyep]

Im at a loss as to why there are so many magnetic variables, i need help!

What is the magnetic variance for -31 degrees, 151 35 E??

I have maps here but they're all 1972 Datum!

I use my compass to help polar align to get me roughly in the right area and i broke my last compass and i forgot the MV value. (some say Magnetic North is 12 degrees, some say 20 degrees others say 31 degrees East of True North...... )

Thanks for your help guys/gals!
Cheers!