question: What must be used for accurate measurement on the composition of gases at a high vacuums ?
answer: mass spectrometer must be used in conjunction with the ionization gauge
turker_answer: A mass spectrometer must be used in conjunction with the ionization gauge in order to achieve an accurate measurement of the composition of gases at a high vacuums .
rule-based: Mass spectrometer must be used in conjunction with the ionization gauge must be used for accurate measurement on the composition of gases at a high vacuums .