FYI for those with older GPS systems
www.amsa.gov.au/about/regulations-and-standards/marine-notices#cancelled
Select to expand quoteTrek said..
Theres a map here that corrects the errors, and those of magnetic pole reversal:
There are no poles just a wall of ice that stops us falling off the edge 
If you do have a clock problem try replacing antenna first in many devices the clock is in the antenna not the head unit
for instance older j r c units can be updated this way
