Hi, I'm Greg (Indy-Tech). Welcome to JustAnswer. I'm reviewing your question now, and will post back with your reply ASAP.Rgds Greg.
The B in the mileage is the trip A and B giving you two trip mileage counters .
Just press the button and it will go to vehicle mileage, press again it will go to trip A, press again will go to trip B.
Need further assistance with this issue then please get back to me with the reply box below .After rating there is no further cost for any other question relating this issue .Kind regards Greg