Hi Simon - welcome to the forum.
The ScanGauge is an excellent tool, or you could build your own MPGuino, if you're the DIY sort.
Is this your car?
Seems like they could have made the aerodynamics even better if they'd not gone for the "faux notchback" look!
I was just having a conversation about Citroens with my neighbour a couple of hours ago. (He's been stopping by regularly to chat, watching the progress on my
Kammback construction.) There was one in town today for a bit car show - probably a 70's DS - and he commented on its apparently good aerodynamics.
Darin