What figures were you looking at? Grid Reference or Lat Long?mattsccm wrote: ↑9 Apr 2021, 8:14pm I plonked 4 Garmin GPS on the bonnet of my Land Rover once whilst green laning. They all said different things. I knew where I was by the OS map (road junction scarily close to a cross of grid lines) . None were correct with nearly half a mile between the extremes.
The spherical approximation of the Earth in use by GPS (WGS84) is different to that used by OS (OSGB36) and there's a discrepancy which can be 100s of metres.