What is your intrepretation (for those driving cars with the nav system), on what the Best MPG # means on the Consumption bar chart screen?

From reading the manual, it's confusing.

The Average MPG # beside it makes sense: this seems to be your average MPG since the last reset. I intend to never reset this so that it will show a lifetime average.

But then the manual seems to say that the Best MPG # is not displayed until you press Reset, which doesn't make much sense to me.

Anyone with actual experience driving a nav model know how it works, for sure?