Air/Fuel ratio monitor measures the air/fuel ratio of a running engine. It is made up of two major components, an oxygen sensor and a display unit. The oxygen sensor must be mounted in the exhaust system slightly downstream of where all manifold runners merge. This location gives the highest exhaust temperatures and provides a sampling of all the cylinders on that manifold. The sensor sniffs the exhaust and measures the amount of oxygen present in the spent gases. This air/fuel ratio monitor will allow an engine to be tuned to optimum performance very quickly. This is of particular interest for race and performance vehicles and this new technology is much more accurate than exhaust gas temperature equipment.