Usually, the measurement of low vacuum and high vacuum cannot be done with a vacuum gauge, but a composite vacuum gauge should be used, and the ionization and thermocouple composite vacuum gauges are used more. Its measurement range is 13.33--666.6×10-8Pa. The thermocouple vacuum gauge measures the low vacuum of (10-1--10-3)×133.32Pa; the ionization vacuum gauge measures the high vacuum of 133.32×10-3--666.6×10-8Pa. The composite vacuum gauge is equipped with a thermocouple gauge and an ionization gauge, which are respectively connected to the vacuum system. Through the knob, the two gauges can be heated and selected for use.