It's global, but that doesn't mean it's the same everywhere - I'm fairly certain the reason my TT GPS didn't lock south of equator is because there's a bug in its processing software. A north/south problem like that isn't impossible (I used to work with a slightly different kind of orbital processing years back). In any case, I'll be doing some more testing on that (I'll bring several GPS units south of equator - including the TT one, if I can find a way to pack it that won't accidentally switch it on during transport).