ELI5: Explain Like I'm 5

Air-fuel ratio meter

An air-fuel ratio meter is a tool used to measure the amount of air and fuel that enters an engine. It works by measuring the amount of oxygen in a sample of exhaust gas. From this, the air-fuel ratio meter can tell how much air and fuel have been combined to create the exhaust gas. This information can help mechanics adjust the engine to make sure it is running as efficiently and safely as possible.