The Edelbrock Air / Fuel Ratio Monitor is used to adjust all carburation circuits including idle, cruise and power. The oxygen sensor is installed in the exhaust pipe and the electronic display is connected. When the engine is running, the actual air / fuel ratio is continuously displayed. This monitor directly indicates air / fuel ratios from approximately 12 to 15: 1. It works great for RVs or any application where frequent altitude and climate changes are encountered. It is not recommended for use with leaded fuels or alcohol.