A/F gauges that hook up to your stock O2 sensor are narrow band and will not give you a constant reading, unless at WOT, so they're basically useless for tuning part-throttle. They're basically just good as an indicator of an overly lean or overly rich condition during WOT acceleration. GReddy makes an A/F ratio meter with a semi-wideband O2 that will work better thn your typical Autometer unit. If you have more money, you can dish out for a wideband O2 sensor and display unit, but those are pretty expensive, and dyno shops usually have wideband O2's that you can rent to tune with.