sorry to bother you with a question you have probabally heard 10,000 times, but i cant seem to find a more detailed solution on how to fix the gps offset problem in china.

I have heard to modify the settings of gmsup to china or change the MapID, but i dont know how to do either of those things? How do you do them?

I am using ppc garmin mobile xt and would like it to be accurate. thanks