Is this the MFA display or the main speedo/mileometer? I think you're talking about the MFA, the trip computer.
You do know that there are two memory banks on the trip computer? The button underneath the right-hand stalk toggles between the two, Bank 1 is the trip bank, and resets to zero after a couple of hours or so stationary. Bank 2 carries on counting until you reset manually by holding the button for a few seconds.
I use bank 2 for fuel consumption calculations, resetting it every time I fill the tank.
On the MFA display there is a little number at the top right, either 1 or 2, indicating which bank is being displayed.