The speed indicated on the electronic display (GPS screen) is not the speed determined by the GPS signal, but rather from the vehicle speed sensor - the same one that powers the analog speedo. You can confirm this by disconnecting the speed sensor - both the analog and digital speedos will indicate zero. My 2018 SVTC is off by 9 km/h at 100 km/hour speed (when the speedos read 100, I'm actually only going 91 km/h as confirmed by a real GPS and also my car speedometer). I use a Garmin Zumo for actual speed and reliable directions.