I just picked up a Garmin Nuvi 205W. It has a pretty cool speedo and odometer function on it. I've known my speedo has been off for a while due to rearend gear change. I installed an adapter a couple of years ago and got it closer, now I've verified I'm 3-4 miles/hour slow on the low end and 5-6 slow at the top end. Better than I had thought. I'll have to fill up and take a road trip with GPS and find out what my actual MPG is.
