An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed. It was developed by Robert Bosch GmbH during the late 1960s under the supervision of Dr. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1990 and significantly reduced the mass of the ceramic sensing element, as well as incorporating the heater within the ceramic structure. This resulted in a sensor that started sooner and responded faster. The most common application is to measure the exhaust-gas concentration of oxygen for internal combustion engines in automobiles and other vehicles in order to calculate and, if required, dynamically adjust the air-fuel ratio so that catalytic converters can work optimally, and also determine whether the converter is performing properly or not. An oxygen sensor will typically generate up to about 0.9 volt when the fuel mixture is rich and there is little unburned oxygen in the exhaust. Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers, which find extensive use in medical applications such as anesthesia monitors, respirators and oxygen concentrators. Divers use oxygen sensors (and often call them ppO2 sensors) to measure the partial pressure of oxygen in their breathing gas. Open circuit scuba divers test the gas before diving as the mixture remains unchanged during the dive and partial pressure changes due to pressure are simply predictable, while mixed gas rebreather divers must monitor the partial pressure of oxygen in the breathing loop throughout the dive, as it changes and must be controlled to stay within acceptable bounds. Oxygen sensors are also used in hypoxic air fire prevention systems to continuously monitor the oxygen concentration inside the protected volumes. There are many different ways of measuring oxygen. These include technologies such as zirconia, electrochemical (also known as galvanic), infrared, ultrasonic, paramagnetic, and very recently, laser methods. Automotive applications Automotive oxygen sensors, colloquially known as O2 ("ō two") sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, whether the