the unit gets reflashed. You tell them what mods you have done to your car. That's one reason why I went with the ssafc. Every car reacts differently to mods. Two cars can have the same mods, install the unichip and get different results. There is nothing better than dyno tuning a car, even street tuning is good. The whole reflash thing you have to do with the unichip is ok, but there is no real time air/fuel monitoring. It's good for most bolt ons, but once you start going into bigger turbos, custom manifolds, meth injection, it really wouldn't work that well. But at the same time, most would swap to a standalone setup by then.