1. enter PU page, you need to select a channel with known coord, i.e. channel 10 or 30 or 45 etc
2. the selected PU channel with correct latlon should have a visual reference (i.e. at the coord of channel 10, there's a factory etc)
3. then when you fly over the reference (i.e. factory), press the PU button again, your INS pos should be fixed to the correct one and err eliminated