It piggybacks onto the J3 port and hooks up to a laptop. You can change just about any of the parameters you want. You can datalog, tune on the fly, switch tunes on the fly, store about 8 different tunes. If you ever get to where you ti]hink your tune is pervect and you want to put the QH on another car, you can burn a Moates chip and stick it on the J3 and you're ff and running without the umbilical cord. It's kind of like the twEECer but immeasurably better and costs about half as much. Last time I looked, they were going for about $250 new.