Use of two types of current measuring devices galvanometer and vacuum tube amplifier, with an ionization gauge shows that the stable sensitivity, $\left(\frac{\frac{\mathrm{positive}\mathrm{ion}\mathrm{current}}{\mathrm{mm}\mathrm{gas}\mathrm{pressure}}}{\mathrm{current}\mathrm{fluctuation}}\right),$ is greater for low electron emission densities thus favoring the use of the amplifier with its greater current sensitivity. Such factors as electrode size, relative potentials, electron emission, interelectrode leakage, type of inlet, gas adsorption, surface charges, temperature changes, B.K. oscillations, and variations of pumping speed which influence the design of a gauge are discussed and an arrangement to fulfill the necessary requirements is described. Performance tests show the gauge to be capable of measuring beam pressure changes at least as small as 3×${10}^{-11\mathrm{}}$ mm of mercury or approximately 3×${10}^9$ mercury atoms per square centimeter per second.

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