FWIW : If you have the Navi Option - The average is your average consumption since the last time you pressed reset. When you press reset that average value goes to best and average starts over until reset again. Reset all will reset both average and best.

I use the MID (info panel inside speedo) to see my tank average - it resets automatically when you pump gas...

 

The BEST is for **** people (I guess I am one of them) that likes to see what their best tank was. I always reset my avg after each fillup. The BEST only changes when the AVG is higher than the BEST.

 

Correct.