Electrical Analog 2 Inch Blue/White Air Fuel Ratio Gauge. Monitors your A/F ratio in real time. This is one of the easiest gauges to install. It picks up the signal from your stock O2 sensor and displays the reading instantly on the Gauge. This Gauge is most useful to alert the driver to a lean condition under wide-open throttle when the computer adjustments are in a loop and no longer quickly changing. This gauge also incorporates an opening ceremony/needle sweep each time the vehicle is started.