The Extorr XT residual gas analyzer is a quadrupole mass spectrometer complete with a built-in Pirani gauge and Ion gauge. It is an essential measuring device which may be used in any vacuum system. The Extorr XT residual gas analyzer (RGA) models come in 100, 200 and 300 amu packages. All RGA models attach to a single 2 3/4 inch flange. Each package has automatic start-up and shut down and will constantly monitor from atmospheric pressure to ultra high vacuum. The built-in Pirani gauge and ion gauge constantly monitor total pressure and regulate and protect the RGA. These functions are seamlessly integrated into the Extorr software package.