It installs a wide band 02 sensor in the front pipe and replaces Harley's useless air temp gauge with something the rider can use, a AFR Gauge telling the rider what his air fuel ratio is in real time while he's riding. The tuner itself is totally programmable and upgradeable using a infrared sensor built into the AFR Gauge, uses Dobeck's load base technology and the AFR Gauge has control buttons that allows the rider to adjust the air fuel ratio alongside the road, once adjusted you shouldn't have to mess with it unless you change air cleaner, pipes or maybe just want to fine tune your fuel mileage a little.