Now you can really watch the ratio of fuel to air in your vehicle with the Intellitronix super bright LED digital air/fuel ratio bargraph gauge!  It is accurate, super bright, and intelligent all in one. 
 
Other features include:

2 1/16 inch diameter, only 1 1/2 inch deep;

Automatic night-dimming;

and In-dash mounting hardware!
 
The Air/Fuel Ratio gauge is a measuring device which provides a more accurate, real-time method of determining the actual ratio of fuel to air in an engine’s combustion chamber by measuring the oxygen content in the exhaust. 
 
To operate properly, the Air/Fuel Ratio gauge requires voltage input from an industry standard narrow-band oxygen sensor. On the gauge face, each LED light bar represents 0.1 Volts input from the sensor. When two red, two yellow, and one green LED are displayed on the gauge, there is approximately a 14.7:1 air-to-fuel mixture. This is the stoichiometric (STOICH) air/fuel ratio, which is the chemically correct ratio and the point of lowest emissions. It is at this position that all of the oxygen and fuel in your engine has been consumed. 
 
When all light bars are displayed, the vehicle is running full rich. When only one or two red bars are displayed, the vehicle is running lean. The combustion is never perfect in the real world and oxygen sensor output changes with temperature and wear, so it is impossible to indicate the exact richness or leanness with a standard narrow-band oxygen sensor. 
The figures shown on the gauge should only be used as a reference point for tuning and evaluation. If your vehicle is computer equipped, you will find that the Air/Fuel Ratio will continually fluctuate at idle and cruising speeds as the computer is rapidly adjusting the air-fuel ratio to reach and sustain the point of lowest emissions. 
 
Also, depending on the type of oxygen sensor you are using, there may be a short lag in time before the gauge begins functioning as some sensors need a moment to reach operating temperature; heated sensors do not rely on exhaust gasses to bring them to operating temperature and will react much quicker. If your vehicle’s performance decreases and the gauge becomes sluggish, it is possible that your oxygen sensor is not working properly.