The SAFC lets you make changes air fuel ratio and view data such as: RPM, Throttle Position, Air flow, and a few others I can't remember off hand. This is cool because not only can you increase performance but you can also use it as a digital gauge and see how much better your car performs after mods. It can display this info in 3 ways, graphs, gauges, or numbers. Unfortunately the Celica has Adaptive Learning Fuel Logic and will eventually counter any changes made to the Air/Fuel ratio after about 10 drive cycles or more (about a week for me). Anyway it still works really well as a digital gauge, a way to measure mod performance, and looks really cool at night! Also if I want my modification to the Air/Fuel ratio to take effect I simply reset the celicas ECU and the car runs faster for a week (good for drag strips). Hope this helps? You can try Apexi's web site for more info. It really is a good product but unfortunately doesn't work quite right for our car.