Description: height of the centre of the exhaust pressure gauge; Name: height of exhaust pressure gauge 
Description: Height of the zero or centre position of the outlet manometer, or other point as defined by the manometer calibration ; Name: Height of the outlet manometer
Description: variable quantity, which is not influenced by the control but is introduced into the control system from outside with the aim of making the final controlled variable follow it in a given relationship; Name: command variable