The 835 VQM is a mass spectrometer that operates from UHV to 10⁻⁵ Torr and accurately measures the gases in the vacuum chamber. The 835 VQM Differential Pump System delivers the advantages of the 835 VQM at higher pressures. The VQM system consists of an autoresonant ion trap mass spectrometer gauge, a VQM Controller and VQM Viewer software that that converts raw data into actionable information. The system is ratiometric, meaning that it determines the ratio of each gas to other gases in a vacuum chamber. It is usually coupled with a total pressure gauge to provide partial pressures of each gas as indication of the quality of the vacuum in the chamber.