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...

2009 BRM/Bisque TCH : UT w/Nav,LA,SR,CQ with PV50 and RX60. CoverCraft Evolution and UVS100;
FormulaOne Pinnacle 35/15/15 Tint ; LLumar Paint Protection; Vinguard.