Tried +tyres +nav +calibration but no info.

Can someone explain the re-calibration of satnav after new tyres and why its needed and how?

Thanks Now - MY11 RRS Autobiography TDV6, Orkney gray, tints, steps, daylight running lamps and allllll the toys!!!
Ex- RRS HSE TDV6 07 Java Black, bi xenon, corner lights, side steps, tints, cool box, smoke side repeats, chrome "sport" boot sill
Ex - Audi A4 Cab 3.0TDi Quattro
Ex - Freelander2 SE TD4
Ex - CRV Auto

Sat Nav uses satellite data to give position.

RRS system also monitors each wheel's rotation. If tyres are deflated for off-road or pressure is changed then so is the rolling radius. Calbration just matches the two feeds up again.