An evaluation has been performed of the precision required to provide indicated pressure repeatability time-to-time and reproducibility controller-to-controller, with respect to the operational parameters of ionization gauge controllers. Gauge sensitivity of Bayard-Alpert type hot cathode ionization gauges has been studied and the dependence upon parameters of operation has been measured and will be displayed graphically. These measurements will allow a user to compare the precision of the userâ?Ts gauge controller to the needs of accurate pressure indication. The independent parameters varied were anode potential and cathode potential, with either cathode end at the cathode bias potential and with the cathode heating voltage applied at either cathode end, while the other variables of operation were held fixed. The fixed parameters were various electron emission currents, various nitrogen pressures, and several gauges. Another issue in ionization gauge operation is measurement of the base pressure of a vacuum chamber by a gauge attached to that chamber which is a continual problem in practical applications. Test data will be shown demonstrating that the magnitude of electron emission can significantly affect the indicated pumpdown rate observed for the chamber, or can significantly affect the steady state value of the indicated base pressure for a practical chamber in the UHV range.