It's pretty accurate, but the cruise control does range from 69-71 as I roll through the hills in that section. I have a speed display on a GPS enabled radar detector that I use to set the cruise at exactly 70 when I am approaching my start point. I don't bother with trying to read the needle at any time.All this science is very intriguing guys, cool. What about the cruise control itself, I mean, on the M6 GT the cruise control is digital, but how reliable is that setting for sure? I mean, I've seen my digital cruise control displaying at 70 mph at the same time that I've seen my GPS displaying 71 or 72 mph, and the needle almost at 71. So are these things really exact, accurate, or just approximations? They don't seem to jive exactly the same with each other, at times anyway, so I wonder if some calibration may be needed for more accurate data. Just wondering.