For engines other than those with fully variable exhaust nozzles, turbine discharge pressure, engine pressure, or engine pressure ratio can be used with good results to indicate or set engine thrust. They vary proportionally to the thrust the engine is developing. Most turbojet and turbofan aircraft today are instrumented for engine pressure ratio. This is the parameter generally used to set or measure engine thrust during takeoff, climb, and cruise. For very accurate thrust measurement, such as during ground trimming of an engine, turbine discharge pressure is often used to measure thrust. In such cases, it is common practice to temporarily connect a turbine discharge pressure indicator to the engine.