But the in-car unit has both GPS (with the antenna being on the roof) as well as wheel speed. Noticeable in longer tunnels with traffic jams that make the speed vary. Then it's clear Google maps takes a random guess at where you are while the in-car system knows how far along you are.
the only time i am paying attention is when off-roading and recording a track, and then its very obvious when the GPS is doing a good or bad job and unplugged from carplay i get a far more accurate track.
