Any system that predicts a service due date is doing arithmetic on an estimate. The estimate can be good. It is still an estimate, and the moment it is displayed like a fact it starts doing damage.
Road trips lie
Drive 900 miles in one week and a naive projection concludes you now drive 900 miles every week. Left alone it will have you due for service in two weeks and shouting about it. The correction is to weight recent readings but clamp how far one unusual gap can move the rate, so a vacation is a bump rather than a new baseline.
And label it, always
The important discipline is not the math, it is the labeling. A computed mileage is shown as an estimate, marked as one, with the option to correct it one tap away. A number the household typed in is shown plainly. Mixing the two — letting a guess sit in the same field as a reading — is how a maintenance record quietly becomes fiction.