Good news is that we will be updating both the iPhone and Android apps in the next few weeks that will improve the odometer estimate shown in the apps:)
How is odometer calculated?
The car odometer and the GOFAR use the same sensor in the vehicle for the calculation of odometer (GOFAR does not use GPS for this calculation). But both are not perfectly accurate so there will be some deviation.
How to get accurate value?
To match back your car's odometer reading with the app, just enter an updated odometer value in the app (from the car health) then start the car and do a trip. (we can attach a screenshot here of the Car Health)
Updating the odometer value in the GOFAR app (in car health) once every few weeks is a good practice that will ensure that the exported data values are accurate. When you do an export, the server actually uses an algorithm using trip data and the entered odometer values to create a very accurate set of data in the export.
The value that you see in the app is just the current estimate (the exported data is more accurate if you enter odometer once in a while). :)