Distance & GPS
Comparing distance measured by the vehicle's odometer with the smartphone's GPS.
Vehicle odometers run ±2% accurate (calibrated to factory wheel size); GPS runs ±1% on a normal route but can fail in tunnels or covered garages. On a 100-km trip, typical divergence is 1–3 km. For the receipt, use GPS when the app captured the whole trip; use the odometer reading when GPS was off or signal was poor.