An air-fuel ratio meter monitors the air–fuel ratio of an internal combustion engine. Also called air–fuel ratio gauge, air–fuel meter, or air–fuel gauge, it reads the voltage output of an oxygen sensor, sometimes also called AFR sensor or lambda sensor. The original narrow-band oxygen sensors became factory installed standard in the late 1970s and early 1980s. In recent years a newer and much more accurate wide-band sensor, though more expensive, has become available.