Yes, you might be right about the volume. I was looking at the buttons here [1] but the volume one looked more like a round push button than a dial. I guess it could be a dial

As to the ring around the number, well I'm more confused going back and looking at it again. Sometimes, like [2] it's a single colour, and others, like [3] it's divided into multiple segments. 12/14mph is slow, so I'd expect to see the ring extend not as far as it does. I'd expect it to extend that far around for speeds like 70mph

Another thought - the little mpg/regen graph is prominent but largely useless. However, if speed and acceleration were added it could be a very useful tool in working out which driving conditions give best economy

[1] http://www.minimallyminimal.com/storage/post-images/doko/d13...

[2] http://www.minimallyminimal.com/storage/post-images/doko/f07...

[3] http://www.minimallyminimal.com/storage/post-images/doko/d10...