We had a diesel Audi A3 some years back, bought brand new, and were offered the opportunity to choose whether we wanted to have a fixed service interval or a flexible one. When I queried how this worked they explained it was based on the type of oil being used. Instead of simply monitoring the mileage or time the car monitors the type of driving and lets you know when it needs servicing. That Audi did 18000 miles before it’s first service.