What is this as it relates to BMW fuel consumption?

[dumkid]

It's quite annoying. Every time I hit 154mph, the little alarm goes off. How am I supposed to get to work with that alarm blaring!?

Set it at 170

 

[wavinwayne]

Average speed during the period of measurement.

This is what it is. I reset it before I left work and watched it fluctuate on the drive home.