Jason, you can keep your scangauges and tachometers, my most valuable instrument is this bird, mounted on the cowl of my Smart car. All this $4 flowerpot bird has to do to tell me everything I need to know about hypermiling is just to flap its set of spring-loaded wings in a particular way.
This is how it works. When the wings are extended, like they are in this picture, I get the best mileage. At highway speed they fold up into a tight V. In a cross wind, one will fold upwards and the other will lay out flat, pointing in the direction of the wind. In a good tailwind, the wings lay out like in the photo sometimes up to 40 mph. On the highway, I'll get behind a line of trucks or cars and the wings will flap, indicating turbulence and reduced drag. If you dare, pulling up close to a truck will cause the wings to drop down, indicating that you are in the low pressure pocket behind the truck. Naughty bird!
Don't you hate it when you spend hundreds of dollars on instruments and some weirdo goes by you at 65 mpg with a stupid bird on his hood and a speedometer and a couple of idiot lights in his dash? Life ain't fair!