its this gay little thing....looks like a radar detector.....they are supposed to tell you what your car will run in the 1/4, supposedly can measure HP, and other stuff. They're very inaccurate.....they claim to be within like .2 seconds on the 1/4 mile times....but when I used it, it was like a full 2-3 seconds off....so I wouldn't hold any truth to the numbers they kick out.

http://www.jeepsunlimited.com/module...article&sid=31