Autometer Air Fuel Ratio Gauge
 
 
This will let me know if my car is either running, lean or rich.  Lean being that there is not enough gas going into the engine and rich meaning that there is too much gas going into the engine.  Stoich is when the engine is having perfect combustion. The right mixture of gas & air is being combusted.

 
 
 
 
 
 
 
 
 
 
 
 
 

All PnP pics are courtesy Jon's Digital Camera.  Good for taking pics of Exotic sport cars and personal photo's in Walmart. :)