Well Actually No Thats Where You are Mixed Up. A/F Tells You your AIR/FUEL RATIOS! EGT tells you your EXHAUST GAS TEMPS. Now running lean is not the only thing that can cause you to run high EGT's. There for Class an A/F gauge would be alot better to have for the sake of Tuning your fuel and boosting up. EGT's are good all around to monitor your car after you start modding or on aftermarket turbo setups. The Greddy A/F Gauge has its own O2 sensor to tap into to get a more accurate reading. Very Nice