The solution is as simple as dividing the initial 55664.9 mileage by 9 and rounding down to the next 0.1 of a mile. That will give the trip mileage of 6184.9, at which point the overall mileage will be 61849.8 but it will display 61849. This happened yesterday (August 2nd) as I drove down the A42 near Ashby. Very satisfying it was too!